Charge pump circuit

ABSTRACT

A bipolar output charge pump circuit having a network of switching paths for selectively connecting an input node and a reference node for connection to an input voltage, a first pair of output nodes and a second pair of output nodes, and two pairs of flying capacitor nodes, and a controller for controlling the switching of the network of switching paths. The controller is operable to control the network of switching paths when in use with two flying capacitors connected to the two pairs of flying capacitor nodes, to provide a first bipolar output voltage at the first pair of output nodes and a second bipolar output voltage at the second pair of bipolar output nodes.

This is a continuation of application Ser. No. 16/988,796, filed Aug.10, 2020, now U.S. Pat. No. 11,043,894, which is a continuation ofapplication Ser. No. 16/450,129, filed Jun. 24, 2019, now U.S. Pat. No.10,819,229, which is a continuation of application Ser. No. 16/023,114,filed Jun. 29, 2018, now U.S. Pat. No. 10,333,395, which is acontinuation of application Ser. No. 15/597,850, filed May 17, 2017, nowU.S. Pat. No. 10,014,769, which is a continuation of application Ser.No. 15/205,439, filed Jul. 8, 2016, now U.S. Pat. No. 9,685,856, whichis a continuation of application Ser. No. 14/542,086, filed Nov. 14,2014, now U.S. Pat. No. 9,391,508, which is a continuation of U.S.application Ser. No. 13/403,450, filed Feb. 23, 2012, now U.S. Pat. No.8,890,604, which is a continuation of U.S. application Ser. No.13/336,795, filed Dec. 23, 2011, now abandoned, which claims the benefitof U.S. Provisional Application No. 61/427,431, filed on Dec. 27, 2010and claims priority to UK Application No. 1021810.5, filed on Dec. 20,2010, the disclosures of which are incorporated by reference herein intheir entireties.

BACKGROUND OF THE INVENTION 1. Field of the Invention

Aspects of the present invention relate to a bipolar output voltagecharge pump circuit and more particularly, they relate to a bipolaroutput voltage charge pump circuit which provides two bipolar outputvoltages, i.e. two pairs of opposite polarity output voltages.

2. Description of the Related Art

Bipolar, i.e. dual rail, output voltage charge pump circuits are a typeof DC-DC converter that utilize transfer and storage capacitors asdevices to respectively transfer and store energy such that theconverter is able to provide, from a unipolar, i.e. single rail, inputvoltage source, a bipolar output voltage that may be different in valuefrom that of the unipolar input voltage.

In use, single bipolar output voltage charge pump circuits may comprisetwo output storage capacitors, typically known as “reservoir capacitors”and one or more energy transfer capacitors, typically known as “flyingcapacitors”. The terminals or connectors of the two “reservoircapacitors” are permanently connected to respective output voltageterminals or nodes. In contrast, the terminals or connectors of the two“flying capacitors” are capable of being switched, in a controlledsequence, to input or output voltage terminals or nodes or to the otherflying capacitor terminals or nodes.

For example, a known single bipolar output voltage charge pump circuit,as disclosed in the present applicants co-pending UK patent applicationGB 2444985, can provide positive and negative bipolar output voltages(+/−VV/2) that are each equal to half the magnitude of the charge pumpcircuit's unipolar input voltage.

Furthermore, by suitable control, the co-pending UK patent applicationcan also provide positive and negative bipolar output voltages (+/−VV)that are each equal to the magnitude of the charge pump circuit'sunipolar input voltage.

Such a known bipolar output voltage charge pump circuit uses anarrangement, i.e. a network, of switches to control the connection ofthe terminals of the two reservoir capacitors, i.e. the two outputvoltage terminals, and those of the flying capacitors. The flyingcapacitor terminals may be connected by these switches to: the inputvoltage terminal, i.e. the unipolar input voltage; the output voltageterminals, i.e. the bipolar output voltages; a reference terminal, e.g.ground potential; and to one another in order to obtain either thebipolar output voltage +/−VV/2 or +/−VV.

FIG. 1 schematically shows a known audio output chain 10, utilising acharge pump 12. The audio output chain 10 receives input audio signaldata 14 and after processing and amplifying the audio signal, outputs anaudio signal 15. Audio signal 15 may be output to a load (notillustrated) such as headphones, speakers or a line load, possibly via aconnector (not illustrated) such as a mono or stereo jack.

Input audio signal data 14 is first processed in a digital processingblock 16, which is powered by DVDD and DVSS, say 1.2V and ground i.e.0V, giving output binary digital signals with output logic levels equalto DVDD and DVSS. These output logic levels are then level shifted bydigital level shifter 18 to logic levels of VV and VG required to drivethe digital-to-analog converter (DAC) 20, supplied by supplies VV andVG, say 1.8V and ground. The level shifted audio data is then convertedto analog signal data by the DAC 20. The output from the DAC 20 is inputto a first amplifier stage 22, and then onto a second amplifier stage 24which may be a headphone amplifier.

In FIG. 1, the first amplifier stage 22 is powered by the input supplyvoltage VV and a reference voltage VG, say ground. To maximise signalswing in each polarity, the amplifier will be configured so that itsoutput will preferably be biased approximately half way between VV andVG, e.g. at VV/2. However, if the second amplifier stage 24 was alsopowered by the input voltage VV and the reference voltage VG, theamplifier output voltage would again preferably be centred about VV/2.To avoid passing d.c. current though the load, e.g. a speaker with otherterminal grounded, a coupling capacitor would be required in seriesbetween the amplifier output and the load. It is well known in the artthat this series connected coupling capacitor needs to be a large valueto allow adequate bass response, and so tends to be physically large andexpensive. Also on power-up and power down charging this capacitor up toits quiescent voltage of VV/2 is liable to cause audible pops, clicksand other audio artefacts in the audio output signal 15. Techniques areknown to reduce these artefacts, but in practice cannot remove themcompletely, and demands of users for reduced audio artefacts arebecoming ever more stringent.

In order to eliminate the above problems, the circuit of FIG. 1 uses ananalog level shift block 26, to level shift the output from the firstamplifier stage 22 such that the DC quiescent voltage is removed and thesignal out of the second amplifier stage 22 is balanced around zerovolts i.e. ground. A charge pump circuit 12 (or some other bipolarsupply means) is then necessary to provide from a unipolar supply VV, abipolar supply voltage (VP, VN) to the second amplifier stage, to allowthe second amplifier stage to drive the audio output signal 15 at eitherpolarity centered about ground

As can be seen from FIG. 1, the charge pump circuit 12 receives an inputvoltage VV and a reference voltage VG, say ground, and is clocked by aclock signal CK. The charge pump circuit 12 also has a flying capacitor28. The output voltage VP, VN of the charge pump 12 may be +/−α·VV,where a may be 1 or 0.5. In this way, as the audio output signal 15 fromthe second amplifier stage 24 may be balanced around the reference VG,in this case ground potential, the problems associated with having tohave the large coupling capacitor therefore no longer exist.

However, in FIG. 1, it is necessary to perform an analog level shift onthe output signal, centred on VV/2, of the amplifier 22 to bring itsquiescent level down to ground. The analog level shifter 26 is shown asconnected between the output of amplifier 22 and the input of outputdriver stage 24: in some implementations it may comprise a resistornetwork within driver amplifier stage 24, coupled to the output of theamplifier stage 24. This analog level shift is undesirable, as any shiftfrom VV/2 to ground may lead to some voltage drop across someresistance, and hence power will be wasted. The level shift circuititself may introduce audio artefacts on power-up.

Further, charge pump circuits, such as charge pump circuit 12 shown inFIG. 1, are widely used in portable electronics devices where decreasingpower consumption in order to extend battery discharge time is becomingever more important. For an audio chain driving a 16 ohm headphone forexample, typical listening levels in a quiet environment may requireonly 100 μW (40 mV rms or 2.5 mA rms for a 16 ohm headphone). However ifthis current is supplied from a +/−1.5V supply (required to drive 50 mWpeaks for audibility in noisier environments) then the 2.5 mA rmssourced from the 1.5V supply consumes 3.3 mW, i.e. an efficiency of 100μW/3.3 mW=3%. Even if the supply voltage (VP, VN) can be halved usingthe aforesaid known charge pump described above, then the efficiency isstill poor, and reducing the power supply further makes it difficultpractically to get enough voltage headroom for the input stage ofamplifier 24.

Further, especially at low signal levels, the power required to switchthe switching devices of the charge pump may be significant enough todegrade the efficiency.

Furthermore, in order to drive transducers such as piezoelectrictransducers, haptic transducers or backlights for example, bipolaroutput voltages of greater than VV may be required. The same outputchain may be required to drive such loads in some use cases, with aconsequent requirement for operating modes with bipolar output stagesupply voltages greater than VV.

It is desirable to be able to operate a particular charge pump circuit,particularly an integrated circuit implementation, in variousapplications which may have different supply voltages available. Inorder to maintain similar performance with different input supplyvoltages, it is desirable to have a range of step-down and step-upratios available.

Charge pumps that generate a range of output voltages may have multipleflying capacitors. These flying capacitors are generally too large to beaccommodated on-chip, so require dedicated pins on the package a well asoccupying area on the PCB. It is desirable to minimize the number offlying capacitors to reduce cost, package size and board area.

It is therefore desirable to provide an audio output chain and anappropriate charge pump that can supply a wide range of output stagebipolar supply voltages to reduce or minimize power consumption over awide range of output signal levels and input supplies while allowingadequate signal swing in the rest of the chain without requiring anyanalog level-shifting in the signal path, while providing a low cost andsmall physical size.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided acharge pump circuit, comprising: an input node and a reference node forconnection to an input voltage; a first pair of output nodes and asecond pair of output nodes; two pairs of flying capacitor nodes; anetwork of switching paths for interconnecting said nodes; and acontroller operable to control the network of switching paths when inuse with two flying capacitors connected to the two pairs of flyingcapacitor nodes, to provide a first bipolar output voltage at the firstpair of output nodes and a second bipolar output voltage at the secondpair of bipolar output nodes.

The controller may be operable to control the network of switching pathssuch that the first bipolar output voltage is operable to be aselectively variable bipolar output voltage, and the second bipolaroutput voltage a fixed bipolar voltage.

The controller may be operable to control the network of switching pathssuch that the first bipolar output voltage is operable to be aselectively variable first bipolar output voltage, and the secondbipolar output voltage is operable to be a selectively variable secondbipolar output voltage.

The controller may be operable to control the network of switching pathssuch that the first bipolar output voltage is +/−VV/6, where VV is theinput supply voltage to the charge pump circuit.

The controller may be operable to control the network of switching pathssuch that the first bipolar output voltage is +/−(3/2)*VV and the secondbipolar output voltage is +/−VV/2.

The controller may be operable to control the network of switching pathssuch that the voltage across the first flying capacitor is VV/4 and thevoltage across the second flying capacitor is VV/2.

The controller may be operable to control the network of switching pathssuch that the first bipolar output voltage is +/−3VV.

The controller may be operable to control the network of switching pathssuch that the first bipolar output voltage is +/−VV/4 and the secondbipolar output voltage is +/−VV/2.

The controller may be operable to control the network of switching pathssuch that the voltage across the first flying capacitor (CF2) is VV/3and the voltage across the second flying capacitor (CF1) is VV/3.

The controller may be operable to control the network of switching pathssuch that the first bipolar output voltage is +/−VV/3.

The controller may be operable to control the network of switching pathssuch that the first bipolar output voltage is +/−VV/6 and the secondbipolar output voltage is +/−VV/2.

The controller may be operable to control the network of switching pathssuch that the voltage across the first flying capacitor is VV/5 and thevoltage across the second flying capacitor is (⅗)*VV.

The controller may be operable to control the network of switching pathssuch that the first bipolar output voltage is +/−VV/4.

The controller may be operable to control the network of switching pathssuch that the first bipolar output voltage is +/−VV/5.

The controller may be operable to control the network of switching pathssuch that first bipolar output voltage is one of +/−2VV, +/−(3/2)*VV,+/−VV, +/−VV/2, +/−VV/4, or +/−VV/6 and the second bipolar outputvoltage is +/−VV2.

The controller may be operable to control the network of switching pathssuch that first bipolar output voltage is one of +/−3VV, +/−2VV, +/−VV,+/−VV/2, +/−VV/3, +/−VV/4, +/−VV/5 or +/−VV/6 and the second bipolaroutput voltage is +/−VV.

When the controller is operable to control the network of switchingpaths such that the first bipolar output voltage is operable to be aselectively variable bipolar output voltage, and the second bipolaroutput voltage a fixed bipolar voltage, the controller may be operableto control the network of switching paths to provide +/−VV/2 as saidfixed bipolar output voltage, where VV is the input supply voltage tothe charge pump circuit. The controller may operable to control thenetwork of switching paths to selectively provide two or more modes,said variable bipolar output voltage in each mode corresponding to abipolar output voltage of +/−2VV, +/−(3/2)*VV, +/−VV, +/−VV/2, +/−VV/4,or +/−VV/6. The controller may also be operable to control the networkof switching paths to provide +/−VV as said fixed bipolar output voltageand operable to control the network of switching paths to selectivelyprovide two or more modes, the variable bipolar output voltage in eachmode corresponding to a bipolar output voltage of +/−3VV, +/−2VV, +/−VV,+/−VV/2, +/−VV/3, +/−VV/4, +/−VV/5 or +/−VV/6.

When the controller is operable to control the network of switchingpaths such that both the first and second bipolar output voltages areselectively variable, the controller may be operable to control thenetwork of switching paths to selectively provide, the variable secondbipolar output voltage to be +/−VV or +/−VV/2. When the variable secondbipolar output voltage is +/−VV, the controller may be operable tocontrol the network of switching paths to selectively provide one ormore modes, the variable bipolar output voltage in each modecorresponding to a bipolar output voltage of +/−3VV, +/−2VV, +/−VV,+/−VV/2, +/−VV/3, +/−VV/4, +/−VV/5 or +/−VV/6. When the variable secondbipolar output voltage is +/−VV/2, the controller is operable to controlthe network of switching paths to selectively provide one or more modes,the variable bipolar output voltage in each mode corresponding to abipolar output voltage of +/−2VV, +/−(3/2)*VV, +/−VV, +/−VV/2, +/−VV/4,or +/−VV/6.

In use, a first flying capacitor may be connected to first and secondflying capacitor nodes, and a second flying capacitor may be connectedto third and fourth flying capacitor nodes, a first reservoir capacitormay be connected between a first output node and the reference node, asecond reservoir capacitor may be connected between the reference nodeand a second output node, a third reservoir capacitor may be connectedbetween a third output node and the reference node and a fourthreservoir capacitor may be connected between the reference node and afourth output node.

The controller may be operable to control the network of switching pathssuch that, in a first switching state, the first flying capacitor, thesecond flying capacitor and the first reservoir capacitor are connectedin series between the input node and the reference node, the seriesconnected first flying capacitor and the first reservoir capacitor arealso connected in parallel to the third reservoir capacitor between thethird output node and the reference node, and the second flyingcapacitor and the third reservoir capacitor are connected in seriesbetween the input node and the reference node. The controller may beoperable to control the network of switching paths such that the firstbipolar output voltage is +/−VV/4 and the second bipolar output voltageis +/−VV/2.

The controller may be operable to control the network of switching pathssuch that in a second switching state, the first flying capacitor andthe second reservoir capacitor are connected in series, and the secondflying capacitor is connected in parallel with the series connectedfirst flying capacitor and second reservoir capacitor. The controllermay be operable to control the network of switching paths such that thefirst bipolar output is +/−VV/6 and the second bipolar output is+/−VV/2.

At least one output voltage (VP, VN, VQ, VM) of the charge pump circuit,or a voltage difference between any two output voltages, may be comparedwith a threshold level. The threshold may be independent of the inputsupply voltage VV.

The controller may be operable to control the network of switching pathssuch that first reservoir capacitor is recharged when the first outputis smaller in magnitude than a first threshold, the second reservoircapacitor is recharged when the second output is smaller in magnitudethan a second threshold, the third reservoir capacitor is recharged whenthe third output is smaller in magnitude than a third threshold, and thefourth reservoir capacitor is recharged when the fourth output issmaller in magnitude than a fourth threshold.

According to another aspect of the present invention, there is providedan audio output chain arranged to receive an input audio signal andprocess the audio signal to drive a load, said load comprising at leastone of: a headphone, a speaker, a line load, a haptic transducer, apiezoelectric transducer, or an ultrasonic transducer, the audio outputchain comprising the charge pump circuit according to any precedingclaim.

The controller may be operable to control the switching sequence of thenetwork of switches in dependence on a comparison of at least one of theoutputs of the charge pump, or difference in voltage of a bipolar outputof the charge pump, with a threshold level. The threshold level may beindependent of the input voltage.

The audio output chain may further comprise a charge pump controller,wherein the charge pump controller is operable to receive a controlsignal, the threshold level being dependent on the control signal. Thecontrol signal may be a gain or volume signal.

The controller may be operable to control the network of switching pathssuch that first reservoir capacitor is recharged when the first outputis smaller in magnitude than a first threshold, and the second reservoircapacitor is recharged when the second output is smaller in magnitudethan a second threshold.

The controller may additionally be operable to control the network ofswitching paths such that the third reservoir capacitor is rechargedwhen the third output is smaller in magnitude than a third threshold,and the fourth reservoir capacitor is recharged when the fourth outputis smaller in magnitude than a fourth threshold.

The charge pump controller may be operable to receive an input audiosignal, the threshold level being dependent on the input audio signal.

There is also provided an integrated circuit comprising the above chargepump circuit.

There is also provided an audio device comprising the above charge pumpcircuit. Said device may be at least one of: a battery powered device, aportable device, a personal audio device, a personal video device; amobile telephone, a personal data assistant, a gaming device, a portablecomputing device, a laptop and a satellite navigation system.

According to another aspect of the present invention, there is provideda method of controlling a charge pump circuit to generate a bipolaroutput voltage, the charge pump circuit comprising an input node and areference node for connection to an input voltage, a first pair ofoutput nodes and a second pair of output nodes, two pairs of flyingcapacitor nodes, and a network of switching paths for interconnectingsaid nodes, the method comprising the step of: controlling the networkof switching paths when in use with two flying capacitors connected tothe two pairs of flying capacitor nodes, to provide a first bipolaroutput voltage at the first pair of output nodes and a second bipolaroutput voltage at the second pair of bipolar output nodes.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described withreference to the accompany drawings, of which:

FIG. 1 schematically shows a prior art audio output chain;

FIG. 2 schematically shows a charge pump circuit according to anembodiment of the invention;

FIG. 3 schematically shows the charge pump circuit of FIG. 2 in use inan audio output chain;

FIG. 4a shows a circuit diagram of a switch matrix according to anembodiment of the invention;

FIG. 4b shows a network plan of the switching paths in the switch matrixof FIG. 4 a;

FIG. 5a is a table indicating which of the switching paths in FIG. 4aare closed in a first mode of operation;

FIG. 5b shows the switching phases of the first mode of operation;

FIG. 5c shows the sequencing of phases of the first mode of operation;

FIG. 6a is a table indicating which of the switching paths in FIG. 4aare closed in a second mode of operation;

FIG. 6b shows the switching phases of the second mode of operation;

FIG. 6c shows the sequencing of phases of the second mode of operation;

FIG. 7a is a table indicating which of the switching paths in FIG. 4aare closed in a third mode of operation;

FIG. 7b shows the switching phases of the third mode of operation;

FIG. 8a is a table indicating which of the switching paths in FIG. 4aare closed in a fourth mode of operation;

FIG. 8b shows the switching phases of the fourth mode of operation;

FIG. 8c shows the sequencing of phases of the fourth mode of operation;

FIG. 9a shows a circuit diagram of a switch matrix according to anotherembodiment of the invention;

FIG. 9b shows a network plan of the switching paths in the switch matrixof FIG. 9 a;

FIG. 10a is a table indicating which of the switching paths in FIG. 9aare closed in a fifth mode of operation;

FIG. 10b shows the switching phases of the fifth mode of operation;

FIG. 11a shows a circuit diagram of a switch matrix according to anotherembodiment of the invention;

FIG. 11b shows a network plan of the switching paths in the switchmatrix of FIG. 11 a;

FIG. 12a is a table indicating which of the switching paths in FIG. 11aare closed in a sixth mode of operation;

FIG. 12b shows the switching phases of the sixth mode of operation;

FIG. 13a shows a circuit diagram of a switch matrix according to anotherembodiment of the invention;

FIG. 13b shows a network plan of the switching paths in the switchmatrix of FIG. 13 a;

FIG. 14a is a table indicating which of the switching paths in FIG. 13aare closed in an seventh mode of operation;

FIG. 14b shows the switching phases of the seventh mode of operation;

FIG. 14c shows the sequencing of phases of the seventh mode ofoperation;

FIG. 15a is a table indicating which of the switching paths in FIG. 13aare closed in an eighth mode of operation;

FIG. 15b shows the switching phases of the eighth mode of operation;

FIG. 16a is a table indicating which of the switching paths in FIG. 13aare closed in a ninth mode of operation;

FIG. 16b shows the switching phases of the ninth mode of operation;

FIG. 17a is a table indicating which of the switching paths in FIG. 13aare closed in a tenth mode of operation;

FIG. 17b shows the switching phases of the tenth mode of operation;

FIG. 18a shows a circuit diagram of a switch matrix according to anotherembodiment of the invention;

FIG. 18b shows a network plan of the switching paths in the switchmatrix of FIG. 18 a;

FIG. 19a shows a circuit diagram of a switch matrix according to anotherembodiment of the invention;

FIG. 19b shows a network plan of the switching paths in the switchmatrix of FIG. 19 a;

FIG. 20a is a table indicating which of the switching paths in FIG. 19aare closed in an eleventh mode of operation;

FIG. 20b shows the switching phases of the eleventh mode of operation;

FIG. 21a is a table indicating which of the switching paths in FIG. 19aare closed in a twelfth mode of operation;

FIG. 21b shows the switching phases of the twelfth mode of operation;

FIG. 22a is a table indicating which of the switching paths in FIG. 19aare closed in a thirteenth mode of operation;

FIG. 22b shows the switching phases of the thirteenth mode of operation;

FIG. 23a is a table indicating which of the switching paths in FIG. 19aare closed in a fourteenth mode of operation;

FIG. 23b shows the switching phases of the fourteenth mode of operation;

FIG. 24a is a table indicating which of the switching paths in FIG. 19aare closed in a fifteenth mode of operation;

FIG. 24b shows the switching phases of the fifteenth mode of operation;

FIG. 25a is a table indicating which of the switching paths in FIG. 19aare closed in a sixteenth mode of operation;

FIG. 25b shows the switching phases of the sixteenth mode of operation;

FIG. 26a shows a circuit diagram of a switch matrix according to anotherembodiment of the invention;

FIG. 26b shows a network plan of the switching paths in the switchmatrix of FIG. 26 a;

FIG. 27a is a table indicating which of the switching paths in FIG. 26aare closed in a seventeenth mode of operation;

FIG. 27b shows the switching phases of the seventeenth mode ofoperation;

FIG. 28a shows a circuit diagram of a switch matrix according to anotherembodiment of the invention;

FIG. 28b shows a network plan of the switching paths in the switchmatrix of FIG. 28 a;

FIG. 29a is a table indicating which of the switching paths in FIG. 26aare closed in an eighteenth mode of operation;

FIG. 29b shows the switching phases of the eighteenth mode of operation;

FIG. 30 shows the circuit diagram of switch matrix of FIG. 28a with analternative input supply voltage;

FIG. 31a shows a circuit diagram of a switch matrix according to anotherembodiment of the invention with additional switches provided to reducestress;

FIG. 31b shows a network plan of the switching paths in the switchmatrix of FIG. 31 a;

FIG. 32a schematically shows an output chain comprising the charge pumpcircuit according to embodiments of the present invention;

FIG. 32b schematically shows a feed back circuit that enables chargepump control;

FIG. 32c shows an input signal waveform and corresponding envelope andcharge pump output voltage waveforms;

FIG. 33 shows a cross section of an NMOS switch;

FIG. 34 shows VM and VN switches configured with respective bodyconnections;

FIG. 35 shows an NMOS output stage; and

FIG. 36 shows a CMOS output stage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 schematically shows a charge pump circuit 100 that includes aplurality of nodes and a network of switching paths, i.e. a switchmatrix or network of switches or switching network, 110, for selectiveconnection of the plurality of nodes and a controller 120 forcontrolling the network of switching paths. The charge pump circuit 100includes an input node (VV) for receiving an input voltage, a referencenode (VG) for receiving a reference voltage, a first flying capacitornode (CF2A) and a second flying capacitor node (CF2B) for connectionwith a first flying capacitor (CF2), a third flying capacitor node(CF1A) and a fourth flying capacitor node (CF1B) for connection with asecond flying capacitor (CF1), a first pair of output nodes comprising afirst output node (VP) and a second output node (VN), and a second pairof output nodes comprising a third output node (VQ) and a fourth outputnode (VM).

As shown in FIG. 2 and throughout the figures, the input node VV isshown with a white box with a black cross. Likewise, the reference nodeVG is shown with a black box with a white cross. It should be understoodthat the input node VV, the reference node VG, the first and secondoutput nodes VP, VN and the first to fourth flying capacitor nodes CF1A,CF1B, CF2A, CF2B, are nodes on the charge pump circuit for connection tocomponents/inputs external from the charge pump.

FIG. 2 shows charge pump circuit 100 in use, i.e. with a first flyingcapacitor (CF2) and a second flying capacitor (CF1) connected to thefirst and second (CF2A,CF2B), and third and fourth flying capacitornodes (CF1A,CF1B) respectively. A first reservoir capacitor (CRP) isconnected to the first output node (VP), a second reservoir capacitor(CRN) is connected to the second output node (VN), a third reservoircapacitor (CRQ) is connected to the third output node (VQ) and a fourthreservoir capacitor (CRM) is connected to the fourth output node (VM).The reservoir capacitors are arranged such that in use, the negativeterminals of the first and third (CRP,CRQ) and the positive terminals ofthe second and fourth (CRN,CRM) reservoir capacitors are connected tothe reference voltage.

While the positive and negative terminals on these capacitors, i.e. theterminals which in normal operation will be positive and negative withrespect to each other, are identified as such, these capacitors may bepolarised (e.g. electrolytic) or non-polarised (e.g. ceramic) capacitorsaccording to normal design choice.

In the example shown in FIG. 2, the reference voltage VG is ground,though as would be understood by a person skilled in the art, thereference voltage could be a voltage other than ground.

The controller 120 may control the network of switching paths 110 suchthat the charge pump circuit 100 is operable to provide a first bipolaroutput voltage at the first pair of output nodes and a second bipolarvoltage at the second pair of output nodes.

The term bipolar voltage is to be understood to mean two voltages ofopposite polarity relative to some reference voltage, usually a groundvoltage. The bipolar voltage may be symmetric, i.e. be a pair of equaland opposite voltages, centred about ground, or may be asymmetric, i.e.be a pair of unequal but opposite polarity voltages. However, as wouldbe understood, if a reference voltage other than ground was used, asymmetric bipolar output voltage may be centred around the referencevoltage.

In other words, the charge pump circuit is operable to provide apositive first output voltage at the first output node (VP), a negativefirst output voltage at the second output node (VN), a positive secondoutput voltage at the third output node (VQ) and a negative secondoutput voltage at the fourth output node (VM). The first and secondbipolar output voltages may be the same.

In embodiments of the charge pump circuit 100 described herein, bycontrol of the network of switching paths 110 by the controller 120, thecharge pump circuit 100 may be operable to provide a first bipolaroutput voltage at the first and second output nodes (VP,VN) of one of+/−3VV, +/−2VV, +/−3/2VV, +/−VV, +/−VV/2, +/−VV/3, +/−VV/4, +/−VV/5 or+/−VV/6, where VV is the input voltage.

By control of the network of switching paths 110 by the controller 120,the charge pump circuit 100 may be operable to provide a second bipolaroutput voltage at the third and fourth output nodes (VQ,VM) of one of+/−VV or +/−VV/2, where VV is the input voltage.

Additionally, the controller 120 may selectively control the switchingnetwork 110 to provide a variable, or selectable, first bipolar outputvoltage at the first and second output nodes (VP,VN), while maintaininga fixed second bipolar output voltage at the third and fourth outputnodes (VQ,VN). The switching network 110 may be controlled such that thevariable first bipolar output may be selectable to be one or more of+/−3VV, +/−2VV, +/−3/2VV/2, +/−VV, +/−VV/2, +/−VV/3, +/−VV/4, +/−VV/5 or+/−VV/6. The switching network 110 may be controlled such that the fixedsecond bipolar output may either be fixed to +/−W or be fixed to be+/−VV/2.

Further, the controller 120 may selectively control the switchingnetwork 110 to provide a variable, or selectable, first bipolar outputvoltage at the first and second output nodes (VP,VN), and a variable, orselectable, second bipolar output voltage at the third and fourth outputnodes (VQ,VN). The switching network 110 may be controlled such that thefirst variable first bipolar output may be selectable to be one or moreof +/−3VV, +/−2VV, +/−3/2VV, +/−VV, +/−VV/2, +/−VV/3, +/−VV/4, +/−VV/5or +/−VV/6. The switching network 110 may be controlled such that thesecond bipolar output may be selectable in use to be +/−W or +/−VV/2.

The above voltages may be directly or indirectly selectable by means ofa control signal CP_Control as shown in FIG. 3. The control signalCP_Control may be generated externally, or may be generated within anaudio output chain containing the charge pump 100. The charge pump 100may also receive an externally supplied clock CK, or may generate aclock internally.

It should be understood that the above voltages are nominal voltages.Each nominal voltage is associated with a particular control of theswitch matrix, such that in ideal conditions, that nominal outputvoltage would be achieved. In practice however, the actual outputvoltages may be reduced by effects such as switch resistance and loadcurrent. In some embodiments the charge pump 100 may be regulated tosupply a somewhat reduced voltage, possibly related to a referencevoltage (e.g. a bandgap voltage) independent of VV, which referencevoltage may also vary with time, for example according to the envelopeof some audio signal, although in the absence of such reduction byregulation the charge pump 100 would be capable of generating the abovenominal voltages, i.e. would still be operating in a mode correspondingto one of the nominal voltages. In some embodiments the regulation ofthe charge pump may render an output voltage asymmetric, even though thecharge pump output would otherwise be a symmetric bipolar outputvoltage.

FIG. 3 shows an audio output chain, that includes the charge pumpcircuit 100 of FIG. 2. Elements that are common to FIGS. 1 and 2 aregiven the same reference numerals.

As can be seen in FIG. 3, charge pump 100 is operable to output a firstbipolar output voltage at outputs VP, VN for powering the amplifier 24and to output a second bipolar output voltage at outputs VQ, VM forpowering the amplifier 22 and DAC 20. Therefore, by using the chargepump circuit 100, the need for the level shift 26 of the system shown inFIG. 1 is removed, as the first amplifier stage 22 and the secondamplifier stage 24, can be powered by separate bipolar voltages ofdifferent (or the same) magnitude output from a single charge pump 100so the outputs from DAC 20 and amplifier stages 22 and 24 can all becentred on ground i.e. the reference voltage.

Providing two bipolar output voltages allows one to be adjusted to avoidexcess power consumption or dissipation in the output stage, while theother can be designed to supply adequate headroom for upstream signalsand amplifier circuitry.

FIG. 4a shows a circuit diagram of a switch matrix, in which the networkof switching paths is explicitly shown. FIG. 4a , like FIG. 2, shows theswitch matrix having an input node VV for receiving an input voltage, aground reference node VG, a first output node VP, a second output nodeVN, a third output node VQ and a fourth output node VM. Like FIG. 2,FIG. 4a shows the switch matrix in use with two flying capacitors CF1and CF2 connected to the first, second, third and fourth flyingcapacitor nodes CF2A, CF2B, CF1A, CF1B. The flying capacitors, and thereservoir capacitors, themselves are not part of the switch matrix asdefined, nor generally integrated on the same integrated circuit, butare connected to the switch matrix in use. However, it is envisaged thatin a particular implementation, particularly for very light loads with avery fast switching frequency, the capacitors may be integrated into thesame integrated circuit as the switch matrix and indeed other elementsof the charge pump circuit.

For clarity, the first, second, third and fourth reservoir capacitorsCRP, CRN, CRQ, CRM are omitted from FIG. 4a , although it would beunderstood by the skilled person that, in use: a first reservoircapacitor CRP would be connected between the first output node VP and areference node VG; a second reservoir capacitor CRN would be connectedbetween the reference node VG and the second output node VN; a thirdreservoir capacitor CRQ would be connected between the third output nodeVQ and the reference node VG; and a fourth reservoir capacitor CRM wouldbe connected between the reference node VG and the fourth output nodeVM.

In FIG. 4a , one embodiment of the network of switching paths isexplicitly shown. The network of switching paths in FIG. 4a comprisesthirteen switching paths for connecting the various nodes together.Although each switching path in FIG. 4a is shown comprising a singleelement, as would be understood by the skilled person, each switchingpath may comprise a number of discrete switches, e.g. single MOSswitches, or MOS transmission gates, or may be a T-switch or the like asdescribed below, e.g. comprising such discrete switches. The switchingpaths provided in FIG. 4a are:

-   -   A first switching path S2AVP for connecting the first flying        capacitor node (CF2A) to the first output node VP;    -   A second switching path S2AVV for connecting the first flying        capacitor node CF2A to the input node VV;    -   A third switching path S2AVG for connecting the first flying        capacitor node CF2A to the reference node VG;    -   A fourth switching path S2BVN for connecting the second flying        capacitor node CF2B to the second output node VN;    -   A fifth switching path S2BVP for connecting the second flying        capacitor node CF2B to the first output node VP;    -   A sixth switching path S2BVG for connecting the second flying        capacitor node CF2B to the reference node VG;    -   A seventh switching path S1AVQ for connecting the third flying        capacitor node CF1A to the third output node VQ;    -   An eighth switching path S1AVV for connecting the third flying        capacitor node CF1A to the input node VV;    -   A ninth switching path S1AVG for connecting the third flying        capacitor node CF1A to the reference node VG;    -   A tenth switching path S1BVM for connecting the fourth flying        capacitor node CF1B to the fourth output node VM;    -   An eleventh switching path S1BVQ for connecting the fourth        flying capacitor node CF1B to the third output node VQ;    -   A twelfth switching path S1BVG for connecting the fourth flying        capacitor node CF1B to the reference node VG; and    -   A thirteenth switching path S1B2A for connecting the first        flying capacitor node CF2A to the fourth flying capacitor node        CF1B.

Although FIG. 4a is shown with the above thirteen listed switchingpaths, one or more of the switching paths may be removed from thecircuit if not required to provide the desired functionality, i.e. ifnot required in any of the operational modes anticipated in a particularimplementation.

FIG. 4b shows a network plan of the switching paths in the switch matrixof FIG. 4a . Essentially, FIG. 4b shows more clearly the pairs of nodesbetween which there are provided respective switching paths.

Operation of various embodiments of the charge pump circuitry 100 invarious modes of operation is explained below. A mode of operationdenotes a class of embodiments generating a certain pair of bipolarvoltages using a particular set of switching paths.

Each mode of operation involves sequencing though various phases ofoperation, termed Ph1, Ph2, etc., where each phase employs some or allof the available switching paths.

The set of switching paths employed in each phase are described as aswitching state, denoted as e.g. P1, P2 a or P37 c, or possibly acombination of switching states, denoted as e.g. P1+P2 a, P3 x+P37 c.The phases employed in a mode may be sequenced in a chosen one of aplurality of possible repeated sequences, or the sequence may bemodified from one cycle to another according to factors such as varyingload current demand.

In the descriptions of the modes of operation that follow, the switchingstates involved in each mode are shown schematically in figures such asFIG. 5b . Tables such as FIG. 5a are also provided to illustrate whichswitching paths are used (marked with a “1”) and which are not used(marked with a “0”) for each of the switching states of a mode. Tablessuch as FIG. 5c then show possible sequences of phases, i.e.combinations of switching states in various orders. Various networks ofswitching paths are shown in figures such as FIG. 4a , suitable foroperation in various sets of modes. If some possible modes are notrequired in use, there may be switching paths which are never employed:these may either just be always turned off or may be omitted from thephysical implementation to leave a set of switching paths with fewerswitching paths, saving space and cost.

In each mode, the output voltages are derived algebraically. Thenomenclature V(CF1) is used for the voltage between the positive plateand negative plate of CF1, and similarly for V(CF2). The input andoutput supply node voltages are just referred to by the same name as therespective nodes VP, VQ, etc for simplicity, though might be consideredas V(CRP), V(CRQ) etc.

In a first mode of operation, the switch matrix of FIG. 4a may beoperable to provide a first bipolar output voltage of +/−VV/4 at thefirst and second output nodes (VP,VN), and a second bipolar outputvoltage of +/−VV/2 at the third and fourth output nodes (VQ,VM).

FIG. 5b illustrates one embodiment of a plurality of switching states ofthe charge pump of FIG. 4a which can be used to provide the abovevoltages at the output nodes.

In a first switching state, labelled P1 in FIG. 5b , the first flyingcapacitor CF2, the second flying capacitor CF1 and the first reservoircapacitor CRP are connected in series between the input node VV and thereference node VG, the series connected first flying capacitor CF2 andthe first reservoir capacitor CRP are also connected in parallel to thethird reservoir capacitor CRQ between the third output node VQ and thereference node VG, and the second flying capacitor CF1 and the thirdreservoir capacitor CRQ are connected in series between the input nodeVV and the reference node VG. This is achieved by closing the S1AVVswitching path, the S1B2A switching path, the S2BVP switching path andthe S1BVQ switching path.

In a second state P2 n, the first flying capacitor CF2 and the secondreservoir capacitor CRN are connected in parallel between the referencenode VG and the second output node VN. This is achieved by closing theS2AVG switching path and the S2BVN switching path.

In a third state P2 q, the second flying capacitor CF1 and the thirdreservoir capacitor CRQ are connected in parallel between the thirdoutput node VQ and the reference node VG. This is achieved by closingthe S1BVG switching path and the S1AVQ switching path.

In a fourth state P2 p, the first flying capacitor CF2 and the firstreservoir capacitor CRP are connected in parallel between the firstoutput node VP and the reference node VG. This is achieved by closingthe S2AVP switching path and the S2BVG switching path.

In a fifth state P2 m, the second flying capacitor CF1 and the fourthreservoir capacitor CRM are connected in parallel between the referencenode VG and the fourth output node VM. This is achieved by closing theS1AVG switching path and the S1BVM switching path.

From inspection of FIG. 5b , the steady-state output voltages may bederived as follows by assuming there is negligible droop on eachcapacitor, so the voltage across each capacitor remains constantthroughout the various phases.

In state P1, V(CF1)+VQ=VV. From state P2 q, V(CF1)=VQ. ThusV(CF1)=VV/2=VQ.

Similarly, from state P1, VP+V(CF2)+V(CF1)=VV. But V(CF1)=VV/2 and fromstate P2 p, V(CF2)=VP so VP+VP+VV/2=VV, so VP=VV/4=V(CF2).

In states P2 n and P2 m CRN and CRM are charged to −V(CF2) and −V(CF1)respectively, i.e. −VV/4 and −VV/2 respectively.

FIG. 5a is a table showing which switching paths of the charge pump ofFIG. 4a are used in each above state of this mode. In common with othermodes of operation, the various states may be sequenced in a variety ofways, FIG. 5c is a table showing possible sequences a, b, c, . . . ofthese phases.

For instance each state may be sequenced sequentially, one state in eachswitching phase per sequence a or b or indeed any other order of thesestates, possibly including P1 in more than one phase of each cycle toallow more frequent recharging from input supply VV. However preferablystates may be sequenced in combination in a single switching phase. Forexample either of state P2 p and P2 n may be sequenced in combinationwith either of states P2 q and P2 m e.g. per sequences d or e, againpossibly with more frequent appearances of P1 e.g. sequence f.

Also some of the states may be omitted or replaced in particular cyclesaccording to load demand and the consequent droop over time of thevoltages stored on the reservoir capacitors droop. For instance P1 maybe sequenced in one phase of each two-phase cycle, and in the otherphase of each cycle (either P2 p or P2 n) and (either P2 q or P2 m) arechosen based on a detection of which member of each pair of outputvoltages (VP, VN) and (VQ, VM) respectively has drooped the most, asillustrated by sequence g. Indeed if there were little droop on both VQand VM, say, then neither P2 q nor P2 m need be selected until the droopaccumulates enough to make it worth expending the switching energyinvolved.

In a second mode of operation, the switch matrix of FIG. 4a may also beoperable to provide a first bipolar output voltage of +/−VV at the firstand second output node (VP,VN), and a second bipolar output voltage of+/−VV/2 at the third and fourth output nodes (VQ,VM).

FIG. 6b illustrates one embodiment of a plurality of switching states ofthe charge pump of FIG. 4a which can be used to provide the abovevoltages at the output nodes.

In a first switching state, labelled PA in FIG. 6b , the first flyingcapacitor CF2 and the first reservoir capacitor CRP are connected inparallel between the input node VV and the reference node VG. This isachieved by closing the S2AVV switching path, the S2AVP switching pathand the S2BVG switching path. In this phase, as the first flyingcapacitor CF2 and the first reservoir capacitor CRP are connected inparallel between the input node VV and the reference node VG, both thefirst flying capacitor CF2 and the first reservoir capacitor CRP arecharged to VV. This provides a positive voltage of +VV at the outputnode VP.

In a second state, labelled as PB in FIG. 6b , the first flyingcapacitor CF2 and the second reservoir capacitor CRN are connected inparallel between the reference node VG and the second output node VN.This is achieved by closing the S2AVG switching path and the S2BVNswitching path. In this phase, as the first flying capacitor CF2 wascharged to VV in the first state and the first flying capacitor CF2 andthe second reservoir capacitor CRN are connected in parallel, the secondreservoir capacitor is also charged to VV. As the second reservoircapacitor is connected with its positive plate to the reference node VG,a negative voltage of −VV is provided at the second output node VN.

In a third state, labelled as P1 in FIG. 6b , the second flyingcapacitor CF1 and the third reservoir capacitor CRQ are connected inseries between the input node VV and the reference node VG. This isachieved by closing the S1AVV switching path and the S1BVQ switchingpath.

In a fourth state, labelled as P2 in FIG. 6b , the second flyingcapacitor CF1 and the third reservoir capacitor CRQ are connected inparallel between the third output node VQ and the reference node VG.This is achieved by closing the S1BVG switching path and the S1AVQswitching path.

In a fifth state, labelled as P3 in FIG. 6b , the second flyingcapacitor CF1 and the fourth reservoir capacitor CRM are connected inparallel between the reference node VG and the fourth output node VM.This is achieved by closing the S1AVG switching path and the S1BVMswitching path.

From inspection of FIG. 6b , the steady-state output voltages may bederived as follows. In state P1, V(CF1)+VQ=VV. But from state P2,V(CF1)=VQ. Thus V(CF1)=VV/2=VQ. In state P3 CRM is charged to −V(CF2),i.e. −VV/2 so VM=−VV/2.

FIG. 6a is a table showing which switching paths of the charge pump ofFIG. 4a are used in each above state of this mode. FIG. 6c is a tableshowing possible sequences a, b, c, . . . of these phases.

In operation, the controller may sequence these states P1, P2, P3, PA,PB, P1, P2, . . . . However preferably and more efficiently the statesany one of states P1, P2, P3 may be exercised at the same time as eitherof states PA or PB. For instance the sequence may comprise three phases(P1+PA), (P2+PB), (P3+PA), repeatedly. Alternatively the sequence maycomprise four phases (P2+PA), (P1+PB), (P3+PA), (P1+PB), repeatedly: inthis sequence VV is charging one of the flying capacitors in every oneof the four phases, which may help reduce the maximum current spike andreduce losses at high current demands.

A further possibility is to modify the switching sequence on the flyaccording to load current demands or observed droop on the outputs, Forinstance in the third sequence above, after each phase (P1+PB), say,either (P2+PA) or (P3+PA) may be selected, perhaps on the basis ofwhether VQ or VM had drooped the most. Indeed if there were little droopon both VQ and VM, say, then neither P2 nor P3 need be selected in thisphase, and only the state PA exercised, until the droop on VQ or VMaccumulates enough to make it worth expending the switching energyinvolved in including the switching of state P2 or P3

In a third mode of operation, the switch matrix of FIG. 4a may also beoperable to provide a first bipolar output voltage of +/−VV/2 at thefirst and second output node (VP,VN), and a second bipolar outputvoltage of +/−VV/2 at the third and fourth output nodes (VQ,VM).

FIG. 7b illustrates one embodiment of a plurality of switching states ofthe charge pump of FIG. 4a which can be used to provide the abovevoltages at the output nodes.

In a first state, labelled PA in FIG. 7b , the first flying capacitorCF2 and the first reservoir capacitor CRP are connected in parallelbetween the first output node VP and the reference node VG. This isachieved by closing the S2AVP switching path and the S2BVG switchingpath.

In a second state, labelled PB in FIG. 7b , the first flying capacitorCF2 and the second reservoir capacitor CRN are connected in parallelbetween the reference node VG and the second output node VN. This isachieved by closing the S2AVG switching path and the S2BVN switchingpath.

In a third state, labelled PC in FIG. 7b , the first flying capacitorCF2 and the first reservoir capacitor CRP are connected in seriesbetween the input node VV and the reference node VG. To achieve this,the S2AVV switching path and the S2BVP switching path are closed

In a fourth, fifth and sixth states, labelled P1, P2 and P3,respectively, in FIG. 7b , are the same as the third, fourth and fifthstates of the above second mode.

As the states P1, P2, P3 are identical to states P1, P2, P3 of thesecond mode, by the arguments previously stated, the steady statevoltages at output nodes VQ and VM are VQ=VV/2 and VM=−VV/2respectively.

Also the states PC, PA, PB are the same as states P1, P2, P3respectively except that CF1, VQ, and VM are replaced by CF2, VP, and VNrespectively, with consequent changes to the equivalent switching pathsemployed. Thus by similarity, VP=VV/2 and VN=−VV/2.

As with the previous second mode, states PA, PB, PC may be arbitrarilycombined with states P1, P2 and P3 (though to reduce switching currentspike loading of VV, P1 and PC are preferably not simultaneous), orsequenced in a different order, or some of these states may be omittedin particular cycles according to load demand or droop.

In a fourth mode of operation, the switch matrix of FIG. 4a may beoperable to provide a first bipolar output voltage of +/−VV/2 at thefirst and second output node (VP,VN), and a second bipolar outputvoltage of +/−VV/2 at the third and fourth output nodes (VQ,VM). Thefourth mode is operable to provide the same output voltages as the thirdmode, but provides these output voltage using different switching statesand different switching paths, resulting in different flying capacitorvoltages.

FIG. 8b illustrates one embodiment of a plurality of switching states ofthe charge pump of FIG. 4a which can be used to provide the abovevoltages at the output nodes.

In a first state, labelled P1 in FIG. 8b , the first flying capacitorCF2 and the second flying capacitor CF1 are connected in series betweenthe input node VV and the reference node VG, the second flying capacitorCF1 and the third reservoir capacitor CRQ are connected in seriesbetween the input node VV and the reference node VG and the first flyingcapacitor CF2 and the third reservoir capacitor CRQ are connected inparallel between the third output node VQ and the reference node VG.This is achieved by closing the S1AVV switching path, the S1BVQswitching path, the S1B2A switching path and the S2BVG switching path.

In a second state, labelled P2 p in FIG. 8b , the first flying capacitorCF2 and the first reservoir capacitor CRP are connected in parallelbetween the first output node VP and the reference node VG. This isachieved by closing the S2AVP switching path and the S2BVG switchingpath.

In a third state labelled P2 q in FIG. 8b , the second flying capacitorCF1 and the third reservoir capacitor CRQ are connected in parallelbetween the third output node VQ and the reference node VG. This isachieved by closing the S1BVG switching path and the S1AVQ switchingpath.

In a fourth state labelled P2 n in FIG. 8b , the first flying capacitorCF2 and the second reservoir capacitor CRN are connected in parallelbetween the reference node VG and the second output node VN. This isachieved by closing the S2AVG switching path and the S2BVN switchingpath.

In a fifth state labelled P2 m in FIG. 8b , the second flying capacitorCF1 and the fourth reservoir capacitor CRM are connected in parallelbetween the reference node VG and the fourth output node VM. This isachieved by closing the S1AVG switching path and the S1BVM switchingpath.

By similar analysis to the above modes, in state P1, V(CF1)+VQ=VV. Butfrom state P2 q, V(CF1)=VQ. Thus V(CF1)=VV/2=VQ.

Similarly, from state P1, V(CF2)+V(CF1)=VV. But V(CF1)=VV/2 and fromstate P2 p, V(CF2)=VP so VP+VV/2=VV, so VP=VV/2=V(CF2).

In states P2 n and P2 m CRN and CRM are charged to −V(CF2) and −V(CF1)respectively, i.e. both to −VV/2.

FIG. 8a is a table showing which switching paths of the charge pump ofFIG. 4a are used in each above state of this mode. In common with othermodes of operation, the various states may be sequenced in a variety ofways, FIG. 8c is a table showing possible sequences a, b, c, . . . ofthese phases.

For instance each state may be sequenced sequentially, as above inrelation to the first mode of operation. Also as with other modes ofoperation above, some of the states may be repeated, omitted, orreplaced in particular cycles according to load demand and droop.

As described in the above first, second, third and fourth modes, theswitch matrix of FIG. 4a is operable to provide a first bipolar voltageof one of +/−VV, +/−VV/2 or +/−VV/4 at the first pair of output nodes(VP,VN), and to provide a bipolar output voltage of +/−VV/2 at thesecond pair of output nodes (VQ,VM).

Although the above describes individual modes of operation of the switchmatrix separately, and the specific switching paths used in each mode,it should be apparent that when all of the switching paths of FIG. 4aare provided the mode of operation of the switch matrix may be varied inuse, and thus the switch matrix may be operable to provide a firstbipolar voltage that is selectable by the controller from the group of+/−VV, +/−VV/2 or +/−VV/4 at the first pair of output nodes (VP,VN),while providing a fixed bipolar voltage of +/−VV/2 at the second pair ofoutput nodes (VQ,VM).

In other words, the first bipolar output voltage is variable and thesecond bipolar output voltage is fixed. The first bipolar output voltagebeing variable to be +/−VV, +/−VV/2 or +/−VV/4 and the second fixedbipolar output voltage being fixed at +/−VV/2.

FIG. 9a shows a circuit diagram, similar to FIG. 4a , of another switchmatrix, in which the network of switching paths is explicitly shown.This switch matrix comprises all the switches of the switch matrix ofFIG. 4a , but with an additional switching path S1A2B provided betweenthe second flying capacitor terminal CF2B and the third flying capacitorterminal CF1A.

FIG. 9b shows a network plan of the switching paths in the switch matrixof FIG. 9a . Essentially, FIG. 9b shows more clearly the pairs of nodesbetween which there are provided respective switching paths.

As will be understood, as the switch matrix of FIG. 9a contains all ofthe switches of the switch matrix of FIG. 4a , it is also possible tocontrol the switch matrix of FIG. 9a to provide the first, second, thirdand fourth modes as described above.

However, by providing the additional switching path S1A2B, the switchmatrix of FIG. 9a may also be operable in a fifth mode to provide afirst bipolar output voltage of +/−(3/2)·VV at the first and secondoutput node (VP,VN), and a second bipolar output voltage of +/−VV/2 atthe third and fourth output nodes (VQ,VM).

FIG. 10b illustrates one embodiment of a plurality of switching statesof the charge pump of FIG. 9a which can be used to provide the abovevoltages at the output nodes, in a fifth mode.

In a first switching state, labelled P1 in FIG. 10b , the first flyingcapacitor CF2 is connected between the input node VV and the referencenode VG, the second flying capacitor CF1 and the third reservoircapacitor CRQ are connected in series between the input node (VV) andthe reference node VG, and the first flying capacitor CF2 and the seriesconnected second flying capacitor CF1 and third reservoir capacitor CRQare connected in parallel between the input node VV and the referencenode VG. This is achieved by closing the S2AVV switching path, the S2BVGswitching path, the S1AVV switching path, and the S1BVQ switching path.

In a second state, labelled P2 in FIG. 10b , the first flying capacitorCF2 and the second flying capacitor CF1 are connected in series betweenthe first output node VP and the reference node VG, the first flyingcapacitor CF2 and the third reservoir capacitor CRQ are connected inseries between the first output node VP and the reference node VG, andthe second flying capacitor CF1 and the third reservoir capacitor CRQare connected in parallel between the third output node VQ and thereference node VG. This is achieved by closing the S2AVP switching path,the S1AVQ switching path, the S1BVG switching path and the S1A2Bswitching path.

In a third state, labelled P3 in FIG. 10b , the first flying capacitorCF2 and the second flying capacitor CF1 are connected in series betweenthe reference node VG and the second output node VN, the first flyingcapacitor CF2 and the fourth reservoir capacitor CRM are connected inseries between the reference node VG and the second output node VN, andthe second flying capacitor CF1 and the fourth reservoir capacitor CRMare connected in parallel between the reference node VG and the fourthoutput node VN. This is achieved by closing the S2BVN switching path,the S1AVG switching path, the S1BVM switching path and the S1B2Aswitching path.

By similar analysis to previous modes, in state P1, V(CF1)+VQ=VV. Butfrom state P2 b, V(CF1)=VQ. Thus V(CF1)=VV/2=VQ.

Also from state P1, V(CF2)=VV. From state P2, VP=V(CF1)+V(CF2) soVP=VV/2+VV=3VV/2.

Similarly, from state P3, VN=−V(CF2)−V(CF1) so VN=−VV−VV/2=−3VV/2.

Finally from state P3, VM=−V(CF1)=−VV/2.

FIG. 10a is a table showing which switching paths of the charge pump ofFIG. 4a are used in each above state of this mode. In this mode, bothCF1 and CF2 are employed in each state and at different terminalvoltages, so the operations phases Ph1, Ph2, Ph3 just comprise singlestates P1, P2, P3. These states may be sequenced in any order, forexample P1, P2, P3, . . . or P1, P2, P1, P3: for example if there islittle loading on VM and VN, so these outputs exhibit little voltagedroop per cycle, while VP and VQ are more heavily loaded, then thesequence might be modified to P1, P2, P1, P3, P1, P2, P1, P2, P1, P2,P1, P3 . . . .

FIG. 11a shows a circuit diagram, similar to FIG. 4a , of another switchmatrix, in which the network of switching paths is explicitly shown.This switch matrix comprises all the switches of the switch matrix ofFIG. 9a , but with two additional switching paths provided: S1A2Aprovided between the first flying capacitor terminal CF2A and the thirdflying capacitor terminal CF1A, and S1BVV provided between the fourthflying capacitor terminal CF1B and the input node VV. Also, this switchmatrix includes all of the switching paths of the switch matrix of FIG.4a , with the additional switching paths S1A2B, S1A2A and S1BVVprovided.

FIG. 11b shows a network plan of the switching paths in the switchmatrix of FIG. 11a . Essentially, FIG. 11b shows more clearly the pairsof nodes between which there are provided respective switching paths.

As will be understood, as the switch matrix of FIG. 11a contains all ofthe switches of the switch matrix of FIG. 9a , it will also be possibleto control the switch matrix of FIG. 11a to provide the first, second,third, fourth and fifth modes as described above.

By providing the additional switching paths S1A2A and S1BVV, the switchmatrix of FIG. 11a may be operable in a sixth mode to provide a firstbipolar output voltage of +/−2VV at the first and second output node(VP,VN), and a second bipolar output voltage of +/−VV/2 at the third andfourth output nodes (VQ,VM).

FIG. 12b illustrates one embodiment of a plurality of switching statesof the charge pump of FIG. 11a which can be used to provide the abovevoltages at the output nodes in a sixth mode.

In a first state, labelled P1 in FIG. 12b , the second flying capacitorCF1 and the third reservoir capacitor CRQ are connected in seriesbetween the input node VV and the reference node VG. This is achieved byclosing the S1AVV switching path and the S1BVQ switching path.

In a second state, labelled P2 in FIG. 12b , the first flying capacitorCF2 is connected between the reference voltage VG and one terminal ofthe second flying capacitor CF1, the other terminal of the second flyingcapacitor CF1 being connected to the input voltage VV. This is achievedby closing the S2BVG switching path, the S1A2A switching path and theS1BVV switching path.

In a third state, labelled P3 in FIG. 12b , the first flying capacitorCF2 is connected in series with the second flying capacitor CF1 betweenthe first output node VP and the reference node VG, the series connectedfirst and second flying capacitors are connected in parallel with thefirst reservoir capacitor CRP between the first output node VP and thereference node VG, the first flying capacitor CF2 is connected in serieswith the third reservoir capacitor CRQ between the first output node VPand the reference node VG, and the second flying capacitor CF1 isconnected in parallel with the third reservoir capacitor CRQ. This isachieved by closing the S2AVP switching path, the S1BVG switching path,the S1AVQ switching path and the S1A2B switching path.

In a fourth state, labelled P4 in FIG. 12b , the first flying capacitorCF2 and the second flying capacitor CF1 are connected in series betweenthe reference node VG and the second output node VN, the seriesconnected first and second flying capacitors are connected in parallelwith the second reservoir capacitor CRN between the reference node VGand the second output node VN, the first flying capacitor CF2 isconnected in series with the fourth reservoir capacitor CRM between thereference node VG and the second output node VN, and the second flyingcapacitor CF1 is connected in parallel with the fourth reservoircapacitor CRM. This is achieved by closing the S2BVN switching path, theS1B2A switching path, the S1AVG switching path and the S1BVM switchingpath.

The steady-state output voltages may be derived as with other modes frominspection of FIG. 8 b.

In state P1, V(CF1)+VQ=VV. From state P3, V(CF1)=VQ. Thus V(CF1)=W/2=VQ.

From state P2, V(CF2)=VV+V(CF1). But V(CF1)=VV/2 soV(CF2)=VV+VV/2=3VV/2. Hence in state P3,VP=V(CF1)+V(CF2)=VV/2+3VV/2=2·VV.

Similarly from state P4, VN=−V(CF1)−V(CF2)=−2·VV.

Finally, in state P4, VM=−V(CF1)=−VV/2.

FIG. 12a is a table showing which switching paths of the charge pump ofFIG. 4a are used in each above state of this mode. In this mode, bothCF1 and CF2 are employed in each state and at different terminalvoltages, so combinations of these states are not possible, so theoperational phases Ph1, Ph2, Ph3, . . . just comprise single states P1,P2, P3, P4. These states may be sequenced in any order, for example P1,P2, P3, P4 . . . or P1, P4, P1, P2, P3, or omitted in some cyclesaccording to load current demand and droop.

FIG. 13a shows a circuit diagram, similar to FIG. 4a , of another switchmatrix, in which the network of switching paths is explicitly shown.This switch matrix comprises all the switching paths of the switchmatrix of FIG. 4a , but with three additional switching paths provided:S1A2A provided between the first flying capacitor terminal CF2A and thethird flying capacitor terminal CF1A, S1B2B provided between the secondflying capacitor terminal CF2B and the fourth flying capacitor terminalCF1B, and S2AVN provided between the first flying capacitor terminalCF2A and the second output node VN.

FIG. 13b shows a network plan of the switching paths in the switchmatrix of FIG. 13a . Essentially, FIG. 13b shows more clearly the pairsof nodes between which there are provided respective switching paths.

By providing the additional switching paths S1A2A, S1B2B and S2AVN, theswitch matrix of FIG. 13a may be operable to provide a first bipolaroutput voltage of +/−VV/6 at the first and second output node (VP,VN),and a second bipolar output voltage of +/−VV/2 at the third and fourthoutput nodes (VQ,VM). The switch matrix of FIG. 13a may also be operableto provide alternate modes for providing a first bipolar output voltageof +/−VV/2 or +/−VV/4 at the first and second output node (VP,VN), and asecond bipolar output voltage of +/−VV/2 at the third and fourth outputnodes (VQ,VM).

As will be understood, as the switch matrix of FIG. 13a contains all ofthe switches of the switch matrix of FIG. 4a , it is also possible tocontrol the switch matrix of FIG. 13a to provide the first, second,third and fourth modes as described above.

In a seventh mode of operation, the switch matrix of FIG. 13a may beoperable to provide a first bipolar output voltage of +/−VV/6 at thefirst and second output node (VP,VN), and a second bipolar outputvoltage of +/−VV/2 at the third and fourth output nodes (VQ,VM).

FIG. 14b illustrates one embodiment of a plurality of switching statesof the charge pump of FIG. 13a which can be used to provide the abovevoltages at the output nodes.

In a first switching state, labelled P1 in FIG. 14b , the first flyingcapacitor CF2, the second flying capacitor CF1 and the first reservoircapacitor CRP are connected in series between the input node VV and thereference node VG, the series connected first flying capacitor CF2 andthe first reservoir capacitor CRP are also connected in parallel to thethird reservoir capacitor CRQ between the third output node VQ and thereference node VG, and the second flying capacitor CF1 and the thirdreservoir capacitor CRQ are connected in series between the input nodeVV and the reference node VG. This is achieved by closing the S1AVVswitching path, the S1B2A switching path, the S2BVP switching path andthe S1BVQ switching path.

In a second state, labelled P2 c in FIG. 14b , the first reservoircapacitor CRP and the second reservoir capacitor CRN are connected inseries between the first output node VP and the second output node VN,and the first flying capacitor CF2 is connected in parallel between theseries connected first reservoir capacitor CRP and second reservoircapacitor CRN. This is achieved by closing the S2AVP switching path andthe S2BVN switching path. Please note that this phase may be performedsynchronously with either or both of P2 m and P2 q.

In a third state, labelled P2 q in FIG. 14b , the second flyingcapacitor CF1 and the third reservoir capacitor CRQ are connected inparallel between the third output node VQ and the reference node VG.This is achieved by closing the S1BVG switching path and the S1AVQswitching path.

In a fourth state, labelled P2 m in FIG. 14b , the second flyingcapacitor CF1 and the fourth reservoir capacitor CRM are connected inparallel between the reference node VG and the fourth output node VM.This is achieved by closing the S1AVG switching path and the S1BVMswitching path.

In a fifth state, labelled P3 in FIG. 14b , the first flying capacitorCF2 and first reservoir capacitor CRP are connected in series, and thesecond flying capacitor CF1 is connected in parallel with the seriesconnected first flying capacitor CF2 and the first reservoir capacitorCRP. This is achieved by closing the S1A2A switching path, the S1BVGswitching path and the S2BVP switching path.

In a sixth state, labelled P4 in FIG. 14b , the first flying capacitorCF2 and the second reservoir capacitor CRN are connected in series, andthe second flying capacitor CF1 is connected in parallel with the seriesconnected first flying capacitor CF2 and second reservoir capacitor CRN.This is achieved by closing the S1AVG switching path, the S1B2Bswitching path and the S2AVN switching path.

By similar analysis to the above modes, in state P1, V(CF1)+VQ=VV. Butfrom state P2 q, V(CF1)=VQ. Thus V(CF1)=VV/2=VQ.

Also from state P1,

V(CF2)+VP+V(CF1)=VV,

so:

V(CF2)+VP+VV/2=VV,

so

V(CF2)+VP=VV/2.  (x)

But from state P4,

−V(CF1)=−V(CF2)+VN,

so

V(CF2)−VN=V(CF1)=VV/2.  (y)

So, comparing (x) and (y):

VP=−VN.

But from state P2 c

V(CF2)=VP−VN

So

V(CF2)=2·VP

Hence from (above)

V(CF2)+VP=2·VP+VP=VV/2

Hence

V(CF2)=VV/6.

And hence

VP=VV/6; VN=−VV/6

Finally, from state P2 m, VM=−V(CF1)=−VV/2.

Note that P3 is not included in the above analysis, so is not anessential state. Alternatively, it may be shown that P2 q may be omittedif P3 is present.

From the above analysis, embodiments of this mode should include atleast switch states P1, P2 c, P4 and P2 m, and at least one of P3 or P2q. However, since P2 c involves only CF2, P2 c may be combined with oneof P2 q or P2 m if desired. Also since CF1 is connected to the samevoltages in P2 q and P3, P2 q may be combined with P3. Similarly, P4 maybe combined with P2 m. There are thus several possible sequences ofthese states or combinations of states that can implement this mode ofoperation.

FIG. 14a is a table showing which switching paths of the charge pump ofFIG. 10a are used in each state. FIG. 14c is a table illustrating threepossible sequences a, b, c each comprising a four phase sequence Ph12,Ph2, Ph3, Ph4 of these states.

These phases may be sequenced in any order, for example Ph1, Ph2, Ph3,Ph4 . . . or Ph1, Ph2, Ph1, Ph3: In common with other modes variousstates may be repeated, replaced, or omitted in some cycles depending onthe loading or droop on various outputs.

In an eighth mode of operation, the switch matrix of FIG. 13a may alsobe operable to provide a first bipolar output voltage of +/−VV/2 at thefirst and second output node (VP,VN), and a second bipolar outputvoltage of +/−VV/2 at the third and fourth output nodes (VQ,VM). Theeighth mode provides the same output voltages as the third and fourthmodes, but provides these output voltage using a different switchingstate enabled by the additional switches.

FIG. 15b illustrates one embodiment of a plurality of switching statesof the charge pump of FIG. 14a which can be used to provide the abovevoltages at the output nodes.

In a first state, labelled P1 in FIG. 15b , the controller is operableto control the network of switches such that the first flying capacitorCF2 and the second flying capacitor CF1 are connected in parallelbetween the input node VV and the third output node VQ, the first flyingcapacitor CF2 and the third reservoir capacitor CRQ are connected inseries between input node VV and the reference node VG, and the secondflying capacitor CF1 and the third reservoir capacitor CRQ are connectedin series between the input node VV and the reference node VG. This isachieved by closing the S1AVV switching path, the S1BVQ switching path,the S1B2B switching path and the S2AVV switching path.

The second, third, fourth, and fifth switching states P2 q, P2 m, P2 pand P2 n are identical to the respective states of the third and fourthmodes.

By similar analysis to the above modes, in state P1, V(CF1)+VQ=VV. Butfrom state P2 b, VQ=V(CF1). Thus VQ+VQ=VV, so VQ=VV/2, and alsoV(CF1)=VV/2.

Also, from state P1, V(CF2)=V(CF1) so V(CF2)=VV/2.

In states P3 a and P3 b CRN and CRM are charged to −V(CF2) and −V(CF1)respectively, i.e. both VN and VM are equal to −VV/2.

FIG. 15a is a table showing which switching paths of the charge pump ofFIG. 13a are used in each above state of this mode. The various statesmay be sequenced in a variety of ways as described in respect to thesecond and third modes. Also the states P1 of the third mode or statesP1, PC, or P1+PC of the second mode may be interleaved with or replacestate P1 of this mode is some cycles if desired. Also as with othermodes of operation above, some of the states may be repeated, replaced,or omitted in particular cycles according to load demand and droop.

In a ninth mode of operation, the switch matrix of FIG. 13a may beoperable to provide a first bipolar output voltage of +/−VV/2 at thefirst and second output node (VP,VN), and a second bipolar outputvoltage of +/−VV/2 at the third and fourth output nodes (VQ,VM). Theninth mode is operable to provide the same output voltages as the third,fourth and eighth modes, but provides these output voltage usingdifferent switching states.

FIG. 16b illustrates one embodiment of a plurality of switching statesof the charge pump of FIG. 13a which can be used to provide the abovevoltages at the output nodes.

In a first state, labelled P1 in FIG. 16b , the first flying capacitorCF2 and the first reservoir capacitor CRP are connected in seriesbetween the input node VV and the reference node VG, the second flyingcapacitor CF1 and the third reservoir capacitor CRQ are connected inseries between the input node VV and the reference node VG, the firstflying capacitor CF2 and the second flying capacitor CF1 are connectedin parallel between the input node VV and the third output node VQ andthe first reservoir capacitor CRP and the third reservoir capacitor CRQare connected in parallel between the third output node VQ and thereference node VG, and also in parallel between the first output node VPand the reference voltage VG. This is achieved by closing the S1AVVswitching path, the S1BVQ switching path, the S1B2B switching path, theS2AVV switching path and the S2BVP switching path.

In a second state, labelled P2 in FIG. 16b , the first flying capacitorCF2 and the first reservoir capacitor CRP are connected in parallelbetween the first output node VP and the reference node VG, the secondflying capacitor CF1 and the third reservoir capacitor CRQ are connectedin parallel between the third output node VQ and the reference node VG,and the first output node VP and the third output node VQ are connectedtogether. This is achieved by closing the S2AVP switching path, theS2BVG switching path, the S1BVG switching path, the S1AVQ switching pathand the S1A2A switching path.

In a third state, labelled P3 in FIG. 16b , the first flying capacitorCF2 and the second reservoir capacitor CRN are connected in parallelbetween the reference node VG and the second output node VN, secondflying capacitor CF1 and the fourth reservoir capacitor CRM areconnected in parallel between the reference node VG and the fourthoutput node VM, and the second output node and the fourth output nodeare connected together. This is achieved by closing the S2AVG switchingpath, the S2BVN switching path, the S1AVG switching path, the S1BVMswitching path and the S1B2B switching path.

By similar analysis to previous modes, in state P1, V(CF1)+VQ=VV. Butfrom state P2, V(CF1)=VQ. Thus VQ+VQ=VV, so VQ=VV/2, and henceV(CF1)=VV/2.

In state P3 CRM is charged to −V(CF1), i.e. −VV/2. Similarly in stateP1, V(CF2)+VP=VV. But from state P2, V(CF2)=VP. Thus V(CF2)=VV/2 andhence VP=VV/2.

In state P3 CRN is charged to −V(CF2), i.e. −VV/2.

FIG. 16a is a table showing which switching paths of the charge pump ofFIG. 14a are used in each above state of this mode. These states may besequenced in any order, for example P1, P2, P3, . . . or P1, P2, P1, P3:for example if there is little loading on VM and VN, so these outputsexhibit little voltage droop per cycle, while VP and VQ are more heavilyloaded then the sequence might be modified to include more instances ofstate P2 than state P3, for example P1, P2, P1, P3, P1, P2, P1, P2, P1,P2, P1, P3 . . . .

In a tenth mode of operation, the switch matrix of FIG. 13a may beoperable to provide a first bipolar output voltage of +/−VV/4 at thefirst and second output nodes (VP,VN), and a second bipolar outputvoltage of +/−VV/2 at the third and fourth output nodes (VQ,VM). Thetenth mode is operable to provide the same output voltages as the firstmode, but the extra switches available render it possible to provideadditional switching states, labelled P4 and P5 in FIG. 17b , givingmore flexibility in optimising the dynamic behaviour of the charge pumpunder different loads.

FIG. 17b illustrates one embodiment of a plurality of switching statesof the charge pump of FIG. 13a which can be used to provide the abovevoltages at the output nodes.

In a first state, labelled P4 in FIG. 17b , the first flying capacitorCF2 and the first reservoir capacitor CRP are connected in seriesbetween the third output node VQ and the reference node VG, and thesecond flying capacitor CF1, the third reservoir capacitor CRQ and theseries connected first flying capacitor CF2 and first reservoir CRPcapacitor are connected in parallel between the third output node VQ andthe reference node VG. This is achieved by closing the S2BVP switchingpath, the S1AVQ switching path, the S1BVG switching path and the S1A2Aswitching path.

In a second state, labelled P5 in FIG. 17b , the first flying capacitorCF2 and the second reservoir capacitor CRN are connected in seriesbetween the reference node VG and the fourth output node VM, and thesecond flying capacitor CF1, the fourth reservoir capacitor CRM and theseries connected first flying capacitor CF2 and second reservoircapacitor CRN are connected in parallel between the reference node VGand the fourth output node VM. This is achieved by closing the S1AVGswitching path, the S1BVM switching path, the S1B2B switching path andthe S2AVN switching path.

Third to seventh states (labelled P1, P2 n, P2 p, P2 q, and P2 n) areidentical to correspondingly labelled states of the first mode ofoperation. Thus the same analysis proves VQ=V(CF1)=VV/2, VM=−VV/2,VP=V(CF2)=VV/4, and VN=−VV/4.

States P4 and P5 provide additional states, compatible with third toseventh states, i.e. able to maintain the same steady state capacitorvoltages, where for example, in state P5 CF2 can source charge from CRMto help supply a load on VN, even if V(CF2) has drooped below VV/4 dueto heavy loading on a previous phase.

FIG. 17a is a table showing which switching paths of the charge pump ofFIG. 14a are used in each above state of this mode. These states may besequenced in a variety of ways, similar to those described withreference to FIG. 5c , but with additional possibilities arising fromthe enablement of new phases P4 and P5. As with other modes of operationabove, some of the states may be omitted in particular cycles accordingto load demand and droop.

As described in the above seventh, eighth, ninth, and tenth modes, theswitch matrix of FIG. 13a is operable to provide a bipolar outputvoltage of +/−VV/2, +/−VV/4 or +/−VV/6 at the first pair of output nodes(VP,VN), and to provide a bipolar output voltage of +/−VV/2 at thesecond pair of output nodes (VQ,VM). It should also be appreciated, thatas the switch matrix of FIG. 13a also includes all of the switchingpaths of the switch matrix or FIG. 4a , the switch matrix of FIG. 13a isalso operable to provide the above described first, second, third andfourth modes.

In other words, the switch matrix of FIG. 13a is operable to provide afirst bipolar voltage of +/−VV, +/−VV/2, +/−VV/4 or +/−VV/6 at the firstpair of output nodes (VP,VN), and to provide a bipolar output voltage of+/−VV/2 at the second pair of output nodes (VQ,VM).

Although the above describes individual modes of operation of the switchmatrix separately, and the specific switching paths used in each mode,it should be apparent that when all of the switching paths of FIG. 13aare provided the mode of operation of the switch matrix may be varied inuse, and thus the switch matrix may be operable to provide a firstbipolar voltage that is selectable by the controller from the group of+/−VV, +/−VV/2, +/−VV/4 or +/−VV/6 at the first pair of output nodes(VP,VN), while providing a bipolar voltage of +/−VV/2 at the second pairof output nodes (VQ,VM).

In other words, the switch matrix of FIG. 13a is operable to provide avariable first bipolar voltage and a fixed second bipolar output voltage

FIG. 18a shows a circuit diagram, similar to FIG. 4a , of another switchmatrix, in which the network of switching paths is explicitly shown.This switch matrix comprises all the switches of the switch matrix ofFIG. 13a , but with two additional switching paths provided: S1A2Bprovided between the second flying capacitor terminal CF2B and the thirdflying capacitor terminal CF1A, and S1BVV provided between the fourthflying capacitor terminal CF1B and the input node VV.

FIG. 18b shows a network plan of the switching paths in the switchmatrix of FIG. 18a . Essentially, FIG. 18b shows more clearly the pairsof nodes between which there are provided respective switching paths.

By providing the additional switching paths S1A2B and S1BVV, the switchmatrix of FIG. 18a includes all of the switching paths of the switchmatrix of FIG. 13a , with the additional switching paths S1A2B and S1BVVprovided. In other words, the switch matrix of FIG. 18a provides thesame additional switching paths as provided in FIG. 11a . The switchmatrix of FIG. 18a may therefore be operable in the fifth and sixthmodes as described above to provide a first bipolar output voltage of+/−2VV or +/−3/2VV at the first and second output nodes (VP,VN), and asecond bipolar output voltage of +/−VV/2 at the third and fourth outputnodes (VQ,VM).

As will be understood, as the switch matrix of FIG. 18a contains all ofthe switches of the switch matrixes of FIGS. 4a, 9a , 11 a and 13 a, theswitch matrix of FIG. 18a is operable to provide all of the first totenth modes as described above.

As should now be apparent, when all of the switching paths of FIG. 18aare provided, the switch matrix may be operable to provide a firstbipolar voltage that is selectable by the controller from the group of+/−2VV, +/−3/2VV, +/−VV, +/−VV/2, +/−VV/4 or +/−VV/6 at the first pairof output nodes (VP,VN), while providing a fixed bipolar voltage of+/−VV/2 at the second pair of output nodes (VQ,VM).

In other words, the switch matrix of FIG. 18a is operable to provide avariable first bipolar voltage at the first pair of output nodes(VP,VN), and to provide a fixed bipolar output voltage at the secondpair of output nodes (VQ,VM)

The above described embodiments produce +/−VV/2 at one pair of outputs(VQ, VM) and a one or selectable more other bipolar output voltages atthe other pair of outputs (VP, VN). In some systems or devices it ispreferable for the bipolar voltage at VQ, VM to be +/−VV rather than+/−VV/2, for example for a device powered from a lower supply voltageVV.

FIG. 19a shows a circuit diagram, similar to FIG. 4a , of another switchmatrix, in which the network of switching paths is explicitly shown.

FIG. 19b shows a network plan of the switching paths in the switchmatrix of FIG. 19a . Essentially, FIG. 19b shows more clearly the pairsof nodes between which there are provided respective switching paths.

As described below, the switch matrix of FIG. 19a may be operable inmodes to provide a first bipolar output voltage of +/−VV/6, +/−VV/4,+/−VV/3, +/−VV/2, +/−VV, or +/−2*VV at the first and second output nodes(VP,VN), and a second bipolar output voltage of +/−VV at the third andfourth output nodes (VQ,VM).

As will be understood, as the switch matrix of FIG. 19a does not containall of the switches of the switch matrix of FIG. 4a , for example S1BVQ.

In an eleventh mode of operation, the switch matrix of FIG. 19a may beoperable to provide a first bipolar output voltage of +/−VV/4 at thefirst and second output nodes (VP,VN), and a second bipolar outputvoltage of +/−VV at the third and fourth output nodes (VQ,VM).

FIG. 20b illustrates one embodiment of a plurality of switching statesof the charge pump of FIG. 19a which can be used to provide the abovevoltages at the output nodes. FIG. 20b shows the switching pathsactivated in each phase and the resulting respective circuit topologies.

From inspection of FIG. 20b , the steady-state output voltages may bederived similarly to analyses above.

In state P1, V(CF1)+V(CF2)+VP=VV.

But from P3, V(CF1)=V(CF2)+VP, so by substitution for V(CF1),2*V(CF2)+2*VP=VV.

But from state P5, V(CF2)=VP, so by substitution for V(CF2),2*VP+2*VP=4*VP=VV, so hence VP=VV/4, also V(CF2)=VV/4 andV(CF1)=V(CF2)+VP=VV/4+VV/4=VV/2.

From state P4, VN=−(V(CF1)−V(CF2), so VN=−(VV/2−VV/4)=−VV/4.

From state P2, VM=−(V(CF1)+V(CF2)−VN)=−(VV/2+VV/4+VV/4)=−VV.

Finally VQ=VV from the direct connection via S1AVV and S1AVQ in stateP1.

FIG. 20a is a table showing which switching paths of the charge pump ofFIG. 19a are used in each above state of this mode. In common with othermodes of operation, the various states may be sequenced in any order,for example P1, P2, P3, P4, P5 . . . or P1, P4, P1, P2, P1, P3, P1, P5,or some states may be omitted in some cycles according to load currentdemand and droop.

In a twelfth mode of operation, the switch matrix of FIG. 19a may alsobe operable to provide a first bipolar output voltage of +/−VV/6 at thefirst and second output nodes (VP,VN), and a second bipolar outputvoltage of +/−VV at the third and fourth output nodes (VQ,VM).

FIG. 21b illustrates one embodiment of a plurality of switching statesof the charge pump of FIG. 19a which can be used to provide the abovevoltages at the output nodes. FIG. 21b shows the switching pathsactivated in each phase and the resulting respective circuit topologies.

Please note that the first, second, third, and fourth switching statesP1, P2, P3, P4 are identical to the respective states of the previouseleventh mode.

From inspection of FIG. 21b , the steady-state output voltages may bederived similarly to analyses above.

In state P1, V(CF1)+V(CF2)+VP=VV, but in state P3, VP=V(CF1)−V(CF2), so2*V(CF1)=VV, i.e. V(CF1)=VV/2.

In state P3, VP=V(CF1)−V(CF2), but from state P4, VN=−(V(CF1)−V(CF2)),so VN=−VP.

From state P5, V(CF2)=VP−VN, but since VN=−VP, V(CF2)=2*VP.

So returning to state P1, where V(CF1)+V(CF2)+VP=VV, since V(CF1)=VV/2and V(CF2)=2*VP, then VV/2+2*VP+VP=VV, hence VP=VV/6.

Thus V(CF2)=VV/3, and VN=−VV/6.

From state P2, VM=−(V(CF1)+V(CF2)−VN)=VV.

Finally VQ=VV from the direct connection via S1AVV and S1AVQ in stateP1.

FIG. 21a is a table showing which switching paths of the charge pump ofFIG. 19a are used in each above state of this mode. In common with othermodes of operation, the various states may be sequenced in any order,for example P1, P2, P3, P4, P5 . . . or P1, P4, P1, P2, P1, P3, P1, P5,or some states may be repeated, replaced or omitted in some cyclesaccording to load current demand and droop.

In a thirteenth mode of operation, the switch matrix of FIG. 19a mayalso be operable to provide a first bipolar output voltage of +/−VV/3 atthe first and second output nodes (VP,VN), and a second bipolar outputvoltage of +/−VV at the third and fourth output nodes (VQ,VM).

FIG. 22b illustrates one embodiment of a plurality of switching statesof the charge pump of FIG. 19a which can be used to provide the abovevoltages at the output nodes. FIG. 22b shows the switching pathsactivated in each phase and the resulting respective circuit topologies.

Please note that the first and second switching states P1 and P2 areidentical to the respective states of the previous eleventh and twelfthmodes.

From inspection of FIG. 22b , the steady-state output voltages may bederived similarly to analyses above.

In state P1, V(CF1)+V(CF2)+VP=VV, but in state P3, VP=V(CF1)=V(CF2), soV(CF1)=V(CF2)=VP=VV/3.

In state P4, VN=−V(CF1), so VN=−VV/3.

In state P2, VM=−(V(CF1)+V(CF2)−VN), so VM=−VV.

Finally VQ=VV from the direct connection via S1AVV and S1AVQ in state P1

FIG. 22a is a table showing which switching paths of the charge pump ofFigure Ca are used in each above state of this mode. In common withother modes of operation, the various states may be sequenced in anyorder, for example P1, P2, P3, P4 . . . or P1, P4, P1, P2, P1, P3, P1,or some states may be omitted in some cycles according to load currentdemand and droop.

In a fourteenth mode of operation, the switch matrix of FIG. 19a mayalso be operable to provide a first bipolar output voltage of +/−VV/2 atthe first and second output nodes (VP,VN), and a second bipolar outputvoltage of +/−VV at the third and fourth output nodes (VQ,VM).

FIG. 23b illustrates one embodiment of a plurality of switching statesof the charge pump of FIG. 19a which can be used to provide the abovevoltages at the output nodes. FIG. 23b shows the switching pathsactivated in each phase and the resulting respective circuit topologies.

From inspection of FIG. 23b , the steady-state output voltages may bederived similarly to analyses above.

In states P2 and P3, VQ=V(CF1), VM=−V(CF1), VP=V(CF2), VN=−V(CF2).

From P1, V(CF2)+VP=VV, but since V(CF2)=VP, then VP=VV/2 andV(CF2)=VV/2.

Also from P1, V(CF1)=VV, so VQ=V(CF1)=W and VM=−V(CF1)=−VV.

State P4 is an optional state realisable with the switches of FIG. 19a ,in which CF2 is placed in series with CRN: any droop on CF2 thusactually helps bring VN more negative after transition into this state.

FIG. 23a is a table showing which switching paths of the charge pump ofFigure Ca are used in each above state of this mode. In common withother modes of operation, the various states may be sequenced in anyorder, for example P1, P2, P3, . . . or P1, P4, P1, P2, P1, P3, P1, orsome states may be omitted in some cycles according to load currentdemand and droop.

In a fifteenth mode of operation, the switch matrix of FIG. 19a may alsobe operable to provide a first bipolar output voltage of +/−W at thefirst and second output nodes (VP,VN), and a second bipolar outputvoltage of +/−VV at the third and fourth output nodes (VQ,VM).

FIG. 24b illustrates one embodiment of a plurality of switching statesof the charge pump of FIG. 19a which can be used to provide the abovevoltages at the output nodes. FIG. 24b shows the switching pathsactivated in each phase and the resulting respective circuit topologies.

From inspection of FIG. 24b , the steady-state output voltages may bederived similarly to analyses above.

In state P1, V(CF1)=VQ=V(CF2)=VP=VV. In state P2, VN=VM=−V(CF1)=−VV.

FIG. 24a is a table showing which switching paths of the charge pump ofFIG. 19a are used in each above state of this mode. In common with othermodes of operation, the various states may be sequenced in any order,and some states may be omitted in some cycles according to load currentdemand and droop.

In a sixteenth mode of operation, the switch matrix of FIG. 19a may alsobe operable to provide a first bipolar output voltage of +/−2*VV at thefirst and second output nodes (VP,VN), and a second bipolar outputvoltage of +/−VV at the third and fourth output nodes (VQ,VM).

FIG. 25b illustrates one embodiment of a plurality of switching statesof the charge pump of FIG. 19a which can be used to provide the abovevoltages at the output nodes. FIG. 25b shows the switching pathsactivated in each phase and the resulting respective circuit topologies.

From inspection of FIG. 25b , the steady-state output voltages may bederived similarly to analyses above.

In state P1, V(CF1)=V(CF2)=VQ=VV.

In state P2, VP=V(CF1)+V(CF2)=2*VV

In state P3, VM=−V(CF1)=−VV, and VN=−(V(CF1)+V(CF2)=−2*VV.

FIG. 25a is a table showing which switching paths of the charge pump ofFIG. 19a are used in each above state of this mode. In common with othermodes of operation, the various states may be sequenced in any order,and some states may be omitted in some cycles according to load currentdemand and droop. State P4 is an optional extra state using the existingswitches, compatible with the above steady state voltages, which maythus be interleaved with the other states if desired.

As described in the above eleventh to sixteenth modes, the switch matrixof FIG. 19a is operable to provide a bipolar output voltage of +/−2*VV,+/−VV, +/−VV/2, +/−VV/3, +/−VV/4 or +/−VV/6 at the first pair of outputnodes (VP,VN), and to provide a bipolar output voltage of +/−VV at thesecond pair of output nodes (VQ,VM).

Although the above describes individual modes of operation of the switchmatrix separately, and the specific switching paths used in each mode,it should be apparent that when all of the switching paths of FIG. 19aare provided the mode of operation of the switch matrix may be varied inuse, and thus the switch matrix may be operable to provide a firstbipolar voltage that is selectable by the controller from the group of+/−2*VV, +/−VV, +/−VV/2, +/−VV/3, +/−VV/4 or +/−VV/6 at the first pairof output nodes (VP,VN), while providing a bipolar voltage of +/−VV atthe second pair of output nodes (VQ,VM).

In other words, the switch matrix of FIG. 19a is operable to provide avariable first bipolar voltage at the first pair of output nodes(VP,VN), and to provide a fixed bipolar output voltage at the secondpair of output nodes (VQ,VM).

FIG. 26a shows a circuit diagram, similar to FIG. 19a , of anotherswitch matrix, in which the network of switching paths is explicitlyshown. FIG. 26b shows a network plan of the switching paths in theswitch matrix of FIG. 26 a.

This switch matrix comprises all the switches of the switch matrix ofFIG. 19a , but with three additional switching paths provided: S1BVQprovided between the fourth flying capacitor terminal CF1B and the inputnode VV; S2AVV provided between the first flying capacitor terminal CF2Aand the input node VV; and S2AVG provided between the first flyingcapacitor terminal CF2A and the reference node VG.

Also, this switch matrix comprises all the switches of the switch matrixof FIG. 13a , but with one additional switching path S1A2B providedbetween the third flying capacitor terminal CF1A and the second flyingcapacitor terminal CF2B.

Since the switch matrix of FIG. 26a includes all of the switching pathsof the switch matrix of FIG. 19a , it may therefore be operable in theeleventh to sixteenth modes to provide a first bipolar output voltage of+/−2VV, +/−VV, +/−VV/2, +/−VV/3, +/−VV/4 or +/−VV/6 at the first andsecond output nodes (VP,VN), and a second bipolar output voltage of+/−VV at the third and fourth output nodes (VQ,VM).

But also, since the switch matrix of FIG. 26a includes all of theswitching paths of the switch matrix of FIG. 13a , it may therefore beoperable in the first to fourth and seventh to tenth modes to provide afirst bipolar output voltage of +/−VV, +/−VV/2, +/−VV/4 or +/−VV/6 atthe first and second output nodes (VP,VN), and a second bipolar outputvoltage of +/−VV/2 at the third and fourth output nodes (VQ,VM).

Moreover, since this switch matrix includes switching path S1A2B, inaddition to all the switching paths of FIG. 4a , it may also be operablein the fifth mode to provide a first bipolar output voltage of+/−(3/2)*VV at the first and second output nodes (VP,VN), and a secondbipolar output voltage of +/−VV/2 at the third and fourth output nodes(VQ,VM).

Also, as explained below, the switch matrix of FIG. 26a may therefore beoperable in a seventeenth mode to provide a first bipolar output voltageof +/−3VV at the first and second output nodes (VP,VN), and a secondbipolar output voltage of +/−VV at the third and fourth output nodes(VQ,VM).

FIG. 27b illustrates one embodiment of a plurality of switching statesof the charge pump of FIG. 26a which can be used to provide the abovevoltages at the output nodes in a seventeenth mode. FIG. 27b shows theswitching paths activated in each phase and the resulting respectivecircuit topologies.

From inspection of FIG. 27b , the steady-state output voltages may bederived similarly to analyses above.

In state P1, V(CF1)=VV=VQ.

In state P2, V(CF2)=V(CF1)+VQ=2*VV

In state P1, VP=V(CF1)+V(CF2)=VV+2*VV=3*VV

In state P3, VM=−V(CF1)=−VV and VN=−(V(CF1)+V(CF2)=−3*VV.

FIG. 27a is a table showing which switching paths of the charge pump ofFIG. 26a are used in each above state of this mode. In common with othermodes of operation, the various states may be sequenced in any order,and some states may be omitted in some cycles according to load currentdemand and droop.

FIG. 28a shows a circuit diagram, similar to FIG. 26a , of anotherswitch matrix, in which the network of switching paths is explicitlyshown. FIG. 28b shows a network plan of the switching paths in theswitch matrix of FIG. 28 a.

This switch matrix comprises all the switches of the switch matrix ofFIG. 26a , but with two additional switching paths provided: S1BVVprovided between the fourth flying capacitor terminal CF1B and the inputnode VV; S1BVN provided between the fourth flying capacitor terminalCF1B and the output node VN.

Since the switch matrix of FIG. 28a includes all of the switching pathsof the switch matrix of FIG. 26a , it may therefore be operable in theeleventh to seventeenth modes to provide a first bipolar output voltageof +/−3VV, +/−2VV, +/−VV, +/−VV/2, +/−VV/3, +/−VV/4 or +/−VV/6 at thefirst and second output nodes (VP,VN), and a second bipolar outputvoltage of +/−VV at the third and fourth output nodes (VQ,VM), also inthe first to fourth and sixth to tenth modes to provide a first bipolaroutput voltage of +/−(3/2)*VV, +/−VV, +/−VV/2, +/−VV/4 or +/−VV/6 at thefirst and second output nodes (VP,VN), and a second bipolar outputvoltage of +/−VV/2 at the third and fourth output nodes (VQ,VM).

Moreover, since this switch matrix includes switching path S1BVV, it mayalso be operable in the sixth mode to provide a first bipolar outputvoltage of +/−2*VV at the first and second output nodes (VP,VN), and asecond bipolar output voltage of +/−VV/2 at the third and fourth outputnodes (VQ,VM).

Also, as explained below, the switch matrix of FIG. 28a may be operablein an eighteenth mode to provide a first bipolar output voltage of+/−VV/5 at the first and second output nodes (VP,VN), and a secondbipolar output voltage of +/−VV at the third and fourth output nodes(VQ,VM).

FIG. 29b illustrates one embodiment of a plurality of switching statesof the charge pump of FIG. 28a which can be used in an eighteenth modeto provide the above voltages at the output nodes. FIG. 29b shows theswitching paths activated in each phase and the resulting respectivecircuit topologies.

Please note that the first state P1, second state P2, and fourth stateP4 are identical to the first state P1, the second state P2 and thefifth state P5 of FIG. 20 b.

From inspection of FIG. 29b , the steady-state output voltages may bederived similarly to analyses above.

In state P4, VP=CF2, but in state P5=VN=−V(CF2), so VN=−VP.

But in state P3, V(CF1)=V(CF2)+VP−VN, so V(CF1)=3*V(CF2)

From state P1, VV=V(CF1)+V(CF2)+VP

Substituting for V(CF1) and VP,

VV=3*V(CF2)+V(CF2)+V(CF2)=5*VV, so V(CF2)=VV/5.

So from state P4, VP=V(CF2)=VV/5

And from state P5, VN=−V(CF2)=−VV/5

From state P2, VM=−((CF1)+V(CF2)−VN)=−5*(VV/5)=−VV

Finally from the direct connection in state P1, VQ=VV.

FIG. 29a is a table showing which switching paths of the charge pump ofFigure Ca are used in each above state of this mode. In common withother modes of operation, the various states may be sequenced in anyorder, and some states may be omitted in some cycles according to loadcurrent demand and droop.

The switch matrix of FIG. 28a is operable in the above eleventh toeighteenth modes to provide a bipolar output voltage of +/−3*VV,+/−2*VV, +/−VV, +/−VV/2, +/−VV/3, +/−VV/4, +/−VV/5, or +/−VV/6 at thefirst pair of output nodes (VP,VN), while providing a bipolar outputvoltage of +/−VV at the second pair of output nodes (VQ,VM). The switchmatrix of FIG. 28a is also operable in the above first to tenth modes toprovide a bipolar output voltage of +/−2*VV, +/−(3/2)*VV, +/−VV,+/−VV/2, +/−VV/4 or +/−VV/6 at the first pair of output nodes (VP,VN),while providing a bipolar output voltage of +/−VV/2 at the second pairof output nodes (VQ,VM).

Although the above describes the situations of providing single outputvoltages when specific switches of the network of switching paths areutilized, it should be apparent that when all of the switching paths ofFIG. 28a are provided the switch matrix may be operable to provide afirst bipolar voltage that is selectable by the controller from thegroup of +/−3*VV, +/−2*VV, +/−VV, +/−VV/2, +/−VV/3, +/−VV/4, +/−VV/5 or+/−VV/6 at the first pair of output nodes (VP,VN), while providing abipolar voltage of +/−VV at the second pair of output nodes (VQ,VM).Also, the switch matrix may be operable to provide a first bipolarvoltage that is selectable by the controller from the group of +/−2*VV,+/−(3/2)*VV, +/−VV, +/−VV/2, +/−VV/4 or +/−VV/6 at the first pair ofoutput nodes (VP,VN), while providing a bipolar voltage of +/−VV/2 atthe second pair of output nodes (VQ,VM).

In other words, the switch matrix of FIG. 28a is operable to provide avariable first bipolar voltage at the first pair of output nodes(VP,VN), and to provide a fixed or selected bipolar output voltage atthe second pair of output nodes (VQ,VM).

FIG. 30 shows a circuit diagram of a switch matrix, similar to FIG. 28a, of another switch matrix, in which the network of switching paths isexplicitly shown. This switch matrix comprises the switch matrix of FIG.28a , but includes an additional voltage input node VW and switchingpaths S1AVW and S2AVW and optionally S1BVW.

In the case of the controller selecting the additional input voltage VWrather than the input voltage VV, the switching paths S1AVV and S2AVV(and S1BVV where applicable) are left open in all of the switchingphases of the above described first to eighteenth switching modes andthe switching paths S1AVW and S2AVW (and S1BVW where applicable) areused in their place.

These additional switches allow the charge pump to be supplied fromeither VV or VW. If both VV and VW are available at the same time, butare different voltages, this allows a wider range of output voltages,i.e. a combination of those derivable from VV and those derivable fromVW. In some cases, only one may be selected at a time, for example inthe case of a host device being powered from a 5V USB port, or from a 3Vbattery-derived supply in the absence of a USB connection.

In either case, it is preferable to use these parallel switches, ratherthan use an upstream selector switch between VV and VW, to avoid theohmic losses ensuing from a series connection of switches.

Although only a single additional input voltage VW is shown, as would beunderstood by the skilled person, any number of additional inputvoltages could be used by providing appropriate additional switchingpaths, similar to S1AVW and S2AVW (and S1BVW if necessary).

Although only a charge pump based on the charge pump of FIG. 28a isshown in FIG. 30, it should be apparent that the charge pumps of FIG.4a, 9a, 11a, 13a , 18 a, 19 a and 26 a could be modified in a similarway to provide an additional input voltage(s).

As mentioned above, switching paths may comprise either single switchesor possibly equivalent nets comprising a plurality of switches. FIG. 31ashows a circuit diagram of a switch matrix comprising such nets, inwhich the network of switches is explicitly shown. FIG. 31b shows anetwork plan of the switching paths in the switch matrix of FIG. 31 a.

The extra paths can be indentified most clearly by comparing FIG. 31bwith FIG. 13b . The networks shown are similar, but FIG. 31b shows extraswitching paths to those flying capacitor terminals (CF1B, CF2B andCF2A) that are connected to switching paths to VN or VM and added nodesXX, YY, ZZ where other switching paths terminate. For instance in FIG.31b the positive plate of CF2 (node CF2A) is still connected via aswitching path directly to VN, but connected to other switching pathsvia an additional switching path and a node ZZ, where the otherswitching paths previously connected to CF2A now terminate.

FIG. 31a essentially shows the switch matrix of FIG. 13a , but showsthree additional switching paths. The first additional switching path islocated between the first flying capacitor terminal CF2A and a nodelabelled ZZ. The second additional switching path is located between thesecond flying capacitor terminal CF2B and a node labelled ZY. The thirdadditional switching path is located between the fourth flying capacitorterminal CF1B and a node labelled XX.

As can be seen from FIGS. 31a and 31b , the additional switching pathsact to reduce the stress on the switching paths connected to the secondand fourth output nodes (VN,VM). In particular, if these extra switchingpaths are deactivated during states where respective capacitor terminals(e.g. CF2A) are switched to VM or VN, then the nearby terminals of theother, open, switching paths (e.g. S2AVP, S2AVV) from the other end ofthe added switching path (e.g. ZZ) to high voltage nodes VV, VP or VQare no longer connected to the negative voltage VM or VN so are notsubjected to the maximum voltage stress (e.g VV−VN). In such a state,node ZZ would be connected to ground (e.g. by S2AVG). In other words,the additional switching paths act to reduce the maximum voltage acrossany one switching path, and its component physical switches, allowingsmaller or simpler switching structures to be used to implement theseswitching paths, which is advantageous.

These additional switching paths involved in the connection at certainnodes do not affect the connectivity of the flying capacitor nodes tothe voltage nodes VP, VN, VQ, VM, VV, and VG in each switching state.The T-switch arrangements described serve only as a variant method forimplementing the required interconnection of these nodes.

Although only three additional switching paths are provided to reducethe loads, it should be apparent that fewer or more than threeadditional switching paths may be provided to reduce the stress acrossswitching elements of the switch matrix.

FIG. 32a schematically shows an audio output chain 200, comprising acharge pump circuit 202 operable in any one or more of the abovedescribed first to eighteenth modes.

As can be seen from FIG. 32a , the charge pump circuit 202 comprises aswitch matrix or network of switching paths 204 and a switch controller206 for controlling the opening, i.e. enabling, and closing, i.e.disabling, of the various switching paths of the switch matrix 204 so asto provide the desired output voltages. The switch matrix 204 isoperable to selectively connect various nodes together. These nodes maybe terminals on the charge pump circuit for connection with an inputsupply voltage VV, a reference or ground voltage VG, first and secondflying capacitors CF2, CF1, and two pairs of output nodes (VP, VN) and(VQ, VM), when the charge pump circuit is in use. First, second, thirdand fourth reservoir capacitors (CRP, CRN, CRQ, CRM) are arranged in usefor permanent connection to the pairs of output nodes, as describedabove.

Control data 208 is provided to a charge pump control block 210, whichis operable to control the switch controller 206 of the charge pumpcircuit 202. The control data 208 may be a volume control signal, i.e. again signal. The control data may also include shut-down/start-upsignals.

Signal data 212 is provided to a signal path block 214. The signal datamay be digital or analog data, and may have already undergone someupstream (analog or digital) gain. Also, the signal data 212 may beaudio data.

The signal path block 214 receives the signal data 212 at an input 213and couples the signal data to the output driver 218. The output driver218 includes at least an output stage 222 powered from the supplies VP,VN of charge pump 202. In this illustrated example, a precedingamplifier stage 220 is also included which may be powered from suppliesVQ, VM of charge pump 202.

Other circuitry 216, for example a DAC or preamplifier gain stage, maybe provided in the path from input 213 to the output driver 218. Some ofthis other circuitry 216 may be powered from VQ, VM. Indeed in someembodiments some of this preceding circuitry 216 and some or allpreceding stages of 218 may be supplied from VQ, GND rather than VQ, VMfor example to isolate some sensitive stages from possible noise on VM.

Although not shown in FIG. 32a , other circuitry may be provided thatmay or may not be powered from the VQ, VM, outputs of the charge pumpcircuit 202. For example, this other circuitry may comprise digitalfiltering or a digital delay stage that may be powered from digitalsupplies DVDD and DVSS, and possibly digital level-shifting circuitry totranslate logic levels from (DVDD, DVSS) to (VQ, VG) or (VQ, VM).

Further, a gain/volume adjustment, controlled by control data 208, maybe included in the signal path block 214. The gain/volume adjustmentcould be performed digitally, i.e. before a DAC (not illustrated), or inan analog fashion in an analog non-final stage, or in/around the outputdriver 218.

The output 224 of the signal path block 214 is provided to a load (notillustrated) that may be a headphone, speaker, line load, or anothertype of transducer, such as a haptic or piezoelectric transducer orultrasonic transducer, possibly via a connector (not illustrated) suchas a mono or stereo jack. It will therefore be understood that the audiosignal may include data transformed to/from audible sounds, such asmusic and speech and the like but the audio signal may additionally oralternatively comprise ultrasonic data and/or waveforms for drivinghaptic transducers etc and the terms “audio”, “audio signal,” and “audiooutput chain” should be understood accordingly.

The charge pump circuit 202 provides output voltages VP, VN, VQ and VMto power the signal path block. The first output voltage pair (VP, VN)provides a first bipolar voltage to the amplifier output stage 222 andthe second output voltage pair (VQ, VM) may provide a second bipolaroutput voltage to preceding amplifier stage 220 and/or to precedingcircuitry 216.

As described above in the first to eighteenth modes, the nominal firstoutput bipolar voltage may be selectable to be one of: +/−2*VV;+−3/2*VV; +/−VV; +/−VV/2; +/−VV/4; or +/−VV/6 and the nominal secondoutput bipolar voltage may be fixed or selected to be +/−VV/2, or thenominal first output bipolar voltage may be selectable to be one of:+/−3*VV; +/−2*VV; +/−VV; +/−VV/2; +/−VV/3; +/−VV/4; +/−VV/5; or +/−VV/6and the nominal second output bipolar voltage may be fixed or selectedto be +/−VV. In other words, the switch controller may be operable todrive the switch matrix to selectively operate in modes corresponding tothese voltages.

The output voltages (VP, VN, VQ, VM) from charge pump circuit 202 may beselected via charge pump control block 210 based on the input controldata 208. The input control data 208 may be, for example, a volumecontrol signal, that may be independent of the signal data 212. Thecharge pump output voltages (VP, VN, VQ, VM) may then be set to allowadequate headroom, so as to avoid clipping, even for a maximum inputsignal 212 at the specified gain. However if the input signal 212 isconsistently less than maximum expected amplitude, the charge pumpoutput voltages (VP, VN, VQ, VM) will be unnecessarily large, thereforewasting power. Thus, it is advantageous to make some, but preferableall, the charge pump output voltages (VP, VN, VQ, VM) and possibly otheroperational parameters, dependent on the input signal 212, possibly inaddition to the control data 208.

The charge pump control 210 may thus comprise envelope detectioncircuitry to derive a signal Venv indicative of the size of the inputsignal 212. The envelope detection circuitry may take a number of formsthat would be known to a person skilled in the art. The envelopedetection circuitry may, for example, peak detect the input signal,responding rapidly, with a relatively short attack time, to any increasein signal magnitude, but reacting more slowly, with a longer decay time,to any decrease in the input signal. From the signal Venv, the chargepump control 210 may derive and output to the switch controller 206 ofthe charge pump circuit 202 a charge pump control signal CPC.

The control signal CPC may thus be indicative of the size of theenvelope of the signal data 212. The charge pump circuit 202 may then becontrolled based on the control signal CPC to supply correspondingoutput voltages VP, VN and/or VQ, VM. The output voltages of the chargepump circuit 202 may therefore vary with the control signal CPC suchthat a relatively large envelope will lead to a relatively high voltagebeing supplied by the charge pump circuit and conversely, a smallenvelope will lead to a relatively small voltage being supplied by thecharge pump circuit. If the envelope detector circuitry employs arelatively short attack time, this will ensure that rapid spikes in thesignal data 212 will result in a rapid reaction by the envelopedetection circuitry and thus a rapid response can be made so as toincrease the supply voltage, whereas the long decay time will avoidunnecessary switching of the control signal, since it is quite likelythat one high-amplitude signal peak will be followed soon after byanother.

Another example of envelope detection circuitry may comprise a detectorto detect an envelope Venv of the input signal and compare it with somethreshold value. If the detected envelope is below the threshold, thecharge pump circuit 202 may be controlled to provide a relatively lowvoltage, and if the detected envelope is above the threshold, the chargepump circuit 202 will provide a relatively high voltage. To avoidunproductive switching between charge pump voltage levels that mightwaste more energy than it saves, there may be some hysteresis applied tothe comparison, or there may be a minimum timeout imposed before thecharge pump 202 is allowed to be instructed via the control signal CPCto reduce its output voltage(s).

More generally, the envelope detection circuitry may not contain anexplicit peak detector, or actual signal Venv, but the charge pumpcontrol signal may be generated by other means, for instance acomparator coupled without peak detection to the input signal data 212,the comparator having hysteresis and/or a timeout, to effectivelyprovide a type of envelope detection and generate charge pump controlsignal.

Depending on the attack and decay time constants, or the hysteresis ortime out, the signal Venv output from the envelope detector may followthe instantaneous input signal 212 more closely or less closely. It mayessentially track the instantaneous input signal.

As stated above, output driver 218 and/or elements of block 216 maycomprise means for applying gain to what becomes the output signal. Theenvelope detector preferably takes signal data before these gain blocks,so that the input signal is sampled before any processing delay sufferedin the output driver 218 or any circuitry 216 preceding it. Inparticular, circuitry 216 may include a digital interpolation filter(not illustrated) preceding an over-sampling DAC (not illustrated) whichmay introduce a processing delay to the signal. Any such delay willrelax the requirements on the attack time of any peak detector and givethe charge pump 202 more time to ramp up its output voltage(s) in timeto avoid overload due to a sudden signal spike. The envelope detectormay include an asymmetric delay, allowing a quick response to anyincrease in signal level, but a delay before its output is allowed tostart decaying, to avoid the charge pump output decaying before thesignal has propagated through the above processing delay.

However since the swing of the output signal from driver 218 is subjectto this variable gain, the signal sampled upstream is not directlyrepresentative of the output signal. There are several ways ofcorrecting for the effect of this gain applied downstream from the pointwhere the signal is tapped off for application to the envelope detector:an equivalent gain may be inserted in the path between applied inputsignal 212 and the envelope detector within charge pump control block210; the envelope detector output signal may be adjusted in amplitude toallow for the gain applied in the signal path; the threshold levelapplied to the envelope detector output signal may be adjusted tocompensate for the programmed gain.

In other words, the charge pump 202 may be controlled by a charge pumpcontrol signal derived from the input audio signal prior to someapplication of gain controlled by a gain control, or volume, signal, thecharge pump control signal being adjusted according to the gain control,or volume, signal.

The charge pump control block 210 may also have an output forcontrolling the bias current of stages of the amplifier block 218. Forexample, if the signal to be output from driver stage 218 can bepredicted to be small, say on the basis of input signal size or volumesetting, it will be possible to reduce the bias of at least the outputstage without causing too much, or indeed any, distortion. If the outputdriver is set to a low gain, the contribution of preceding stages to thetotal output noise may be reduced, so the input stage bias of thesestages may be reduced without a significant impact on this output noise.These biases may conveniently be controlled via the charge pump controlblock 210.

The control signal from the charge pump control block 210 is provided tothe switch controller 206. The switch controller 206 outputs drivesignals for the switches in the switch matrix 204 of the charge pump202.

The switch controller 206 may control the switch matrix 204, based onthe control signal from the charge pump control 210, to provide thenecessary switch selection and phasing to generate a selected value ofbipolar output voltage at VP, VN. As described above, the nominalbipolar output voltage at VP, VN may be selectable to be +/−2VV,+−3/2VV, +/−VV, +/−VV/2, +/−VV/4 or +/−VV/6. Also, the switch controller206 may control the switch matrix 204, based on the control signal fromthe charge pump control 210, to provide the necessary switch selectionand phasing to generate a selected bipolar output voltage at VQ, VM. Asdescribed above, the nominal bipolar output voltage at VQ, VM mayselectable to be +/−VV or +/−VV/2.

The switch controller 206 may also control the switch matrix 204, tovary other operational parameters of the charge pump, for instance thefrequency or sequencing of switching of the switches in the switchmatrix 204 based on the control data 208, for example a volume controlsignal, or the envelope detector output signal in order to reduceswitching activity when light loading is anticipated but not give riseto excessive ripple when heavy loading is anticipated.

Thus the switching frequency of the switches or the sequence orselection of states or other operational parameters of the charge pump202 may be modulated according to a control signal fed forward from theswitch controller. However in some embodiments the switching of theswitches or other operational parameters may be influenced by signalsfed back from the charge pump output nodes.

Referring to FIG. 32b , this Figure illustrates an embodiment ofcircuitry to enable such control by means of fed back charge pump outputsignals. As in FIG. 32a , a charge pump control block 210 is showncontrolling a charge pump 202 comprising a switch matrix, i.e. a networkof switches, 204 controlled by a switch control block 206 so as togenerate appropriate charge pump bipolar output voltages (VP,VN) and(VQ,VM). In FIG. 32b , more details of an embodiment of the switchcontrol block 206 are explicitly shown. The switch control block 206 isshown to comprise a sequencer 250 which drives switches in the switchmatrix under control of a control logic block 252, which can select adivision ratio N for a clock divider 254 which divides the frequency ofthe incoming clock CK before application to the sequencer 250, and whichcan select one of various stored sequences for the sequencer 250 tosequence through. The control logic 252 also controls the sequenceroutput according to various other inputs by various other outputs whichwill be described in turn below.

As mentioned above, power consumed by the charge pump 202 in switchingthe switches can be reduced by interrupting the switching sequence, onlyactivating the switches when the voltage on a reservoir capacitor (CRP,CRN, CRQ, CRM) has drooped enough to render it worthwhile expending theenergy involved in switching the necessary switches. The voltage droopcan be detected by comparing the actual output voltage with a comparisonvoltage, equal to say a voltage smaller than the target by an amountequal to the tolerable voltage droop, and passing the result of such acomparison as a comparison control signal to the control logic 252 inthe switch controller 206 to interrupt the sequencing.

In FIG. 32b , the charge pump output voltage VP is shown input tocomparator 256, where it is compared to a comparison voltage Vcompselected from one of a plurality of comparison voltages (VenvP, Vref1,Vref2, VV/2-50 mV, VV/4.2) input to a multi-input, multi-output,multiplexer 258. The comparator output signal Vco is input to anappropriate logic in the control logic block shown. This control logicblock 252 can command the sequencer to stop sequencing via an inputlabelled “Stop”.

The comparison may be performed by equivalent means. For example, adifference voltage may be generated by a difference amplifier stage (notillustrated), this difference voltage representing the differencebetween the nominal and actual output voltage, and this differencevoltage may be compared against a reference representing the allowabledroop by a comparator similar to comparator 256.

Similarly, the differential output voltage between two of the outputvoltages, e.g. VP−VN, may be generated by a difference amplifier stage(not illustrated), and this differential voltage compared to a thresholdvoltage.

In either case, the generation of this difference voltage may includesome low pass filtering to smooth out switching spikes or some high passfiltering to make the comparison sensitive to any increase in the slopeof the droop to try and anticipate any increase in loading.

The nominal output voltage of the charge pump circuit described above isa rational fraction, possibly improper, or multiple of the input supplyvoltage, so the comparison voltage Vcomp may be set slightly below thisfraction of the supply voltage, for example the self-explanatorymultiplexer inputs labelled “VV/2-50 mV” or “VV/4.2”. Alternatively, thecomparison voltage Vcomp may be set at an absolute value, for examplethe multiplexer inputs labelled Vref1 and Vref2, perhaps derived from asupply-independent voltage reference such as a bandgap voltagereference, especially if the maximum amplifier output signal is welldefined in terms of absolute voltages, rather than itself being afraction of the supply voltage.

The comparison voltage Vcomp may be fixed, or may be changed during use,for example according to the selected output voltage of the charge pump,for example by the control logic altering the multiplexer connections,or some other alteration of a received reference voltage.

The comparison voltage Vcomp may be variable, for instance based on theoutput Venv of the envelope detector shown in FIG. 32b . If the inputaudio signal 212 becomes small, the reservoir capacitors would then beallowed to discharge down to a similarly small value or some minimumheadroom voltage before being recharged, thus saving switching energy.

Each reservoir capacitor voltage (VQ, VP, VN, VM) may be monitoredindependently, with respect to respective comparison voltages. Chargepump output voltage VN is shown being input to a second comparator 260to generate a second comparator output signal Vco2 for use by thecontrol logic block 252. For convenience VN may be inverted as shownbefore input to the comparator 260, this conveniently allows a commoncomparison voltage to be used for both comparators if a symmetricresponse is desired.

Suitable logic in the switch controller 206 can then determine from Vcoand Vco2 which reservoir capacitor or capacitors are in need ofrecharging, and can thus modulate the switching sequence accordingly soas to cope efficiently with an asymmetric loading. The control logic 252inputs control signals PP and PN that instruct the sequencer to givepriority to switching states which will recharge reservoir capacitorsCRP or CRN respectively. If no reservoir capacitor needs recharging theswitching sequence may be interrupted, i.e. stopped, until a voltage onone of the reservoir capacitors (CRP, CRN, CRQ, CRM) does droop enoughto be worthwhile expending the switching energy needed to recharge it.

If the envelope detector in the charge pump control 210 provides anindication of the magnitude of the input signal 212, this commonmagnitude signal Venv may be used for both positive VP and negative VNcharge pump output voltages. If the envelope detector provides separateindications of the positive and negative envelopes of the input signal,shown as VenvP and VenvN, the comparison voltages used for positive andnegative charge pump output voltages may be controlled independently,and may no longer be balanced around ground especially if the inputsignal 212 is asymmetric. In other words, the actual bipolar outputvoltage may be asymmetric, at least for some time, even if the nominalbipolar voltage of the charge pump operating mode is symmetric.

FIG. 32c illustrates an input signal waveform and corresponding envelopeand charge pump output voltage waveforms for such a case. The positiveenvelope VenvP follows the rapid positive ramp of the signal, but thendecays only slowly after the peak until the next, smaller, peak arrives.The negative envelope VenvN decays to a preset minimum value until thesignal goes appreciably negative. These envelopes are also displacedfrom the input signal by a preset headroom allowance. The charge pumpoutput voltage VP jumps up as the reservoir capacitor CRP is rechargedevery time VP decays down to the envelope VenvP, before decaying backdown to the envelope VenvP at a rate dependent on the signal amplitude,i.e. on the load current. Thus there are frequent recharging events asVP is ramped positive, but relatively few as it ramps negative,particularly when the signal reduces to near zero or negative. (Evenwith a negative signal, some current may still be taken from CRP topower elements of the amplifier output stage). Similarly, CRN is onlyrecharged frequently while the corresponding signal and envelope VenvNare ramping negatively.

At the maximum rate of recharging, the output voltage may rise close tothe nominal output voltage for the set of states, i.e. mode, beingemployed. For instance this maximum charge pump output voltage might be+/−VV/2. To allow occasional bursts of larger signals, or to increaseefficiency if the signal becomes small for a period, the available setof states, i.e. the basic mode of operation of the charge pump, may bealtered, say according to control signal CPC based on a detectedenvelope. For instance, a large envelope may cause a change of mode toone capable of generating +/−VV, or a small envelope may cause a changeof mode to one only capable of generating at most +/−VV/4. In this casethe operation of the charge pump would be affected by both fed forwardand fed back control signals.

Thus the switch controller 206 may control the switch matrix 204, basedon feedback via a comparison control signal or signals derived from acharge pump output voltage, so as to modulate operational parameters ofthe charge pump 202. Thus the switch controller 206 may control theswitch matrix 204, based on a control signal fed forward via the chargepump controller 210 or on a control signal fed back via comparison froma charge pump output voltage. The switch controller 206 may control theswitch matrix 204, based on fed back or fed forward control signal(including the possibility of using a combination of both), so as tomodulate operational parameters of the charge pump 202.

The switch controller 206 may also control the switch matrix 204, basedon a fed back or fed forward control signal, to change the size of someor all switches used to minimize supply drop at heavy loads whilereducing the energy required for each switch transition at light loads.The effective switch size (W/L in the case of a MOS transistor switch)may be changed by activating or deactivating switching of parallelelements of a switch, for instance parallel segments of a MOS switch.FIG. 32c illustrates this possibility by showing the sequencer to have alogic input “As” to indicate whether large or small switches aredesired, and two control wires, e.g. S1A and S1B controlling respectiveportions of each switch, e.g. MOS switch, S1. Normally S1A and S1B willboth be driven with the same signal, activating both portions of S1 whenrequired. But if the control logic 252 asserts input “As” of thesequencer, switch elements corresponding to S1B may be deactivated, thusdecreasing the effective size of S1. The effective sizes of otherswitches, e.g. Sn, may be similarly controlled via similar pairs ofcontrol wires SnA and SnB. The size of all switches may be affected bythe same input “As”, or may be controlled separately via similar inputs,or the size of some switches may remain constant.

The switch controller 206 may also control the switch matrix 204, basedon a fed back or fed forward control signal, to change the magnitude ofa dither applied to the edges of the input clock which controls theclocking of the switching phases. The dither signal may be included soas to reduce spurious tones in the output at light loads, but preserveduty cycle and output impedance at heavy loads, where any such toneswould tend to be randomised by the applied signal, i.e. the audiosignal. The dithering may be controlled by a control signal output fromthe control logic to some circuitry in the clock chain generating theclock CLK used by the sequencer. The control logic may modulate thefactor N by which the input clock CK is divided by the clock divider254, or the dither may be generated by some more complex upstreamcircuitry (not illustrated), for instance to noise shape the ditherspectrum by known techniques.

The output current of the charge pump 202 may also be monitored in orderto modulate operational parameters of the charge pump, for example tochange the switching frequency of the charge pump 202 according to load.

In one embodiment, if a high current is detected, indicating that a lowimpedance is connected, a headphone load may be deduced, in which casethe volume should be restricted to avoid headphone or user overload andhence the output stage supply voltages (VP, VN) from the charge pump 202can be reduced, or if only low currents are detected for a period oftime, indicating connection of only a high impedance load, a line loadcan be assumed, in which case a maximum output swing is required tomaximise signal-to-noise and consequently relatively high supplyvoltages are required to be output by the charge pump 202 while theoutput load current is relatively low, or the device may be assumed tobe powered from the external peripheral or accessory to which the lineoutput is connected, e.g. a docking station, so power efficiency is lessimportant

The current sense block may monitor the voltage drop across one or moreswitches, for example drain-source voltage of a MOS switch in the switchmatrix 204. In the embodiment of FIG. 32b , signals VsnsP and VsnsP areshown emerging from the switch matrix, representing the voltages at eachterminal of a MOS switch of the matrix.

Their difference is then shown being compared by comparator 262 againsta threshold signal to generate a corresponding logic signal for use bythe control logic 252 to modulate the charge pump output voltage orother operational parameters.

The current may also be sensed by circuitry within the output driveramplifier. This may also be used perhaps for functions such as detectinga short to ground on the driver amplifier output. In this case, thesensed current, or a logic signal derived from it indicating excessivecurrent may be transmitted to the charge pump control 210 instead of orin addition to the control logic 252. This is illustrated in FIG. 32b bythe Output Condition Detect Signal input to the charge pump control.Such Output Condition Detect Signals may also be received from othersources, for example from a jack-detect contact on an output jack socketused to connect the driver amplifier to the load.

Although the system illustrated in FIG. 32 illustrates only a singleoutput path from the signal path block 214, it should be understood,that the system of FIG. 32 could be adapted for a stereo output byproviding an additional signal path block 214′ (not illustrated) withappropriate controls. In practice, given the likely correlation betweenleft and right channels, it is not worth the expense of supplying twocharge pumps with independent outputs, so a common control correspondingto the heaviest demand would be applied to a shared charge pump. Ingeneral multiple channels, for instance for surround sound formats, suchas 2.1, 5.1, or 7.1, may share a common charge pump with appropriatecombination of the charge pump control signals.

As stated above, the control data supplied to charge pump control block210 may comprise start-up/shut-down commands. These may be applied viaswitch controller 206 to alter the sequencing or duration of switchingphases or the effective size or resistance (e.g. by modulating the gatedrive voltage applied to a MOS switch) of switches used.

The control data may also comprise commands to ignore any envelopedetection or volume control data and to directly control the settings ofthe switch controller 206, for example to set a fixed charge pumpstep-down ratio, perhaps during system start-up or to allow the envelopedetector to be powered down if the output signal is otherwise known, forexample a fixed amplitude tone. The control data may be derived fromsome sensor, perhaps a mechanical switch or some proximity detector thatdetects when a mobile device is connected to a docking station. The loadmay then by known to be a line load so preferably the output signal willbe increased to maximise signal-to-noise, and in any case the device maybe powered from the docking station so output stage efficiency is nolonger so important. Thus the control data may be set by hardware orsoftware to disable and ignore any envelope detection circuitry.

While FIG. 32b shows circuitry to enable all the various responses tofed-back signals, a particular embodiment would probably only require asubset of these, so the circuit could be simplified, for example byreplacing the multiplexer and most of its reference voltage inputs by asimple hard-wired reference voltage connection.

The switches in the switch matrix 204 may be implemented as MOSswitches. In particular, switches such as S1BVM and S2BVN may beimplemented as NMOS switches. FIG. 33 shows a cross section of an NMOSswitch.

In operation, the NMOS source, drain will be subject to negativevoltages VM, VN. If either of these voltages are more negative than thep substrate, the junction will forward bias, and clamp the node to adiode down from substrate voltage. There is also a possible latch-up andinjection of charge into unexpected nodes e.g. via parasitic npn action.To avoid this, the substrate may be connected to the most negativevoltage on the chip, probably VM or VN. However this will alter thethreshold voltage of every NMOS on the chip, changing as VN changes, andcoupling any noise on VN across the chip. Also in configurations whereVM or VN may at times be the most negative, it would also be necessaryto selectively connect the substrate to the more negative one of the VN,VM.

In order to avoid this, and to allow the substrate to be at ground forthe rest of circuitry, the substrate under VM and VN switches may beisolated using a deep-well (or “triple-well”) option available on modernintegrated circuit fabrication processes. FIG. 34 shows VM and VNswitches configured with respective body connections. The lateral n-welland underlying deep n-well implants isolate these regions. If Vwell isthe most positive potential on the chip, then the junctions to thesen-wells cannot end up forward biased.

Similarly there may also be NMOS inside the amplifiers powered from VMand VN that will need similar NMOS body connections. FIG. 35 shows anNMOS output stage. If VB is constant then this is a Class A sourcefollower; or MN2 gate voltage may be modulated by the input signal on Ato implement a Class AB output stage. In this case, the p-body of MN2 isbiased at VN, so the surrounding n-well may be biased at ground withoutrisk of forward biasing. However the p-body of MN1 is connected to Vout,which may be pulled up near to VP, so the n-well surrounding this p-bodyneeds to be biased to VP (or higher).

FIG. 36 shows a CMOS output stage, again possibly with linkage between Aand B to give a Class AB output stage. The PMOS well may be merged withthe isolating n-well (see figure labelled A) if both are connected toVP, or be separate if MN2 isolating well is connected to e.g. VG. (seefigure labelled B)

As would be apparent to the skilled person, although only eighteen modesof operation are described above, various other modes of operation andvarious other switching sequences for the various phases in each modeoperation could be provided based on the switch matrixes of the presentinvention, without departing from the scope of the present invention.

The above description refers generally to switching paths, it should beunderstood that each switching path may contain a single switch.Alternatively, each switching path may contain any number of discreteswitches as is desired to manage voltage stresses efficiently acrosseach switching path.

The circuits of the charge pump may be controlled by hard-wired logic.But with cheaper, faster processing becoming available, it may bedesirable to implement some functions, for example the envelopedetection, in general purpose DSP hardware loaded with appropriatesoftware algorithms.

The switching paths may use alternative switching structures, such asMEMS relays for example.

It may be convenient for physical layout reasons or for supply noisemanagement reasons to provide more than one physical terminal (forexample package pin, lead, or solder ball) for the input supply and theground, or possibly the charge pump output nodes, where in use theterminals in question are connected together on an underlying substrateor printed circuit board. These terminals would then constitute a singlenode. In some cases the connection may be some distance away from theintegrated circuit, to provide a star ground connection point for aprinted circuit board, but would still constitute a single node.

The above described embodiments use two flying capacitors and associatedswitch matrices or networks of switches. In further embodiments, thecharge pump as described may constitute part of a larger network ofswitches or use more than two flying capacitors, for example to generateyet further voltages. However if these additional switching paths orflying capacitors were removed, the remaining circuitry could still beoperable as described in the above embodiments.

The polarities of voltages on capacitors and outputs in the embodimentsdescribed above have assumed a positive input supply voltage VV (or VW)is applied to the charge pump. Equivalent circuits and operation ispossible with a negative input supply voltage with consequentadjustments to the polarities of voltages.

In summary, embodiments of the present invention provide a pair ofbipolar output voltages from a charge pump, the charge pump being a lowpower, low cost charge pump that is particularly suitable forbattery-powered devices. The described embodiments are also applicablefor higher-power amplifiers, where reduced power dissipation on driversrather than consumption is issue, and the elimination, or at least theminimisation, of audio artefacts is critical.

Although the above describes the invention in relation to audioamplifiers, as will be apparent to the skilled person, the invention isalso applicable to other systems, especially those driving appreciableloads with signals of similar frequencies, e.g. haptic transducerdriving and ultrasonic drivers.

What is claimed is:
 1. A headphone apparatus comprising: an audio outputchain for driving an audio output transducer, the audio output chaincomprising at least a first audio processing stage and a second audioprocessing stage; and a charge pump configured to provide a firstbipolar supply voltage to the first audio processing stage and a secondbipolar supply voltage to the second audio processing stage.
 2. Theheadphone apparatus of claim 1 wherein the first audio processing stagecomprises an amplifier stage.
 3. The headphone apparatus of claim 2wherein the second audio processing stage comprises one of a digitalsignal processor and a digital to analogue converter located upsteam ofthe amplifier stage in the audio output chain.
 4. The headphoneapparatus of claim 2 wherein the charge pump is configured such that thefirst bipolar supply voltage is a selectively variable bipolar voltage,wherein the first bipolar supply voltage is variable independently ofthe second bipolar supply voltage.
 5. The headphone apparatus of claim 4comprising a controller for controlling said charge pump so as toselectively control at least the second bipolar supply voltage based onan indication of a magnitude of an audio signal input processed by theaudio output chain.
 6. The headphone apparatus of claim 5 wherein thecontroller is operable to control the charge pump to control the firstbipolar supply voltage to be one of +/−3VV, +/−2VV, +/−VV, +/−VV/2,+/−VV/3, +/−VV/4, +/−VV/5 or +/−VV/6, where VV is an input voltage tothe charge pump.
 7. The headphone apparatus of claim 6 wherein thecontroller is operable to control the charge pump to control the secondbipolar supply voltage to be one of +/−VV or +/−VV/2.
 8. The headphoneapparatus of claim 6 wherein the controller is operable to control thecharge pump to control the second bipolar supply voltage to be a fixedbipolar output voltage.
 9. The headphone apparatus of claim 1 whereinthe charge pump circuit comprises: an input node and a reference nodefor connection to an input voltage; first and second pairs of outputnodes; two pairs of flying capacitor nodes; a network of switching pathsfor interconnecting said nodes; and a controller operable to control thenetwork of switching paths when in use with two flying capacitorsconnected to the two pairs of flying capacitor nodes to provide saidfirst bipolar supply voltage at the first pair of output nodes and saidsecond bipolar supply voltage at the second pair of output nodes
 10. Theheadphone apparatus of claim 1 further comprising a second audio outputchain for driving a second audio output transducer, wherein the chargepump is further configured to provide said first bipolar supply voltageand said second bipolar supply voltage to audio processing components ofthe second audio output chain.
 11. The headphone apparatus of claim 1wherein the audio output chain is configured to receive a digital audioinput signal.
 12. The headphone apparatus of claim 11 wherein thedigital audio input signal is received wirelessly by the headphoneapparatus.
 13. The headphone apparatus of claim 12 comprising a wirelessreceiver for receiving the digital audio input signal.
 14. The headphoneapparatus of claim 1 wherein the headphone apparatus comprises a stereoheadset.
 15. The headphone apparatus of claim 1 wherein the headphoneapparatus comprises an earbud.
 16. A headphone comprising: an audiooutput path configured to process an input audio signal to generate anaudio driving signal to drive an audio output transducer; and a chargepump configured to provide a first bipolar output voltage to a firstcomponent of the audio output path and a second bipolar output voltageto a second component of the audio output path.
 17. The headphone ofclaim 16 wherein the input audio signal is received wirelessly.
 18. Theheadphone of claim 16 wherein the first component of the audio outputpath is an amplifier stage and wherein the charge pump is operable tocontrollably vary a magnitude of the first bipolar supply voltage,independently of the second bipolar supply voltage, based on anindication of amplitude of the input audio signal.
 19. A headphone setcomprising first and second headphones, wherein each of the first andsecond headphones is a wireless headphone as claimed in claim
 16. 20.The headphone set of claim 19 wherein each of the first and secondheadphones comprises an earbud.
 21. An earbud comprising: an audiooutput path configured to process an input audio signal to generate anaudio driving signal to drive an audio output transducer; and a chargepump for supplying first and second bipolar supply voltage to the audiooutput path, wherein at least the first bipolar supply voltage has amagnitude which is variable based on an indication of amplitude of theinput audio signal.